Cosmetic surgery
Cosmetic surgery was a medical procedure to change the physical appearance of a person, frequently in order to deceive others of the altered individual's true appearance during undercover situations, such as reconnaissance missions. It had some of the same external effects as genetic engineering.

During the 20th century, such procedures were performed almost exclusively by plastic surgeons. ()

Known cosmetic procedures

22nd century 

In 2149, the Klingon scientist Antaak disguised himself as a Mazarite and attended an IME conference on Tiburon. ()

In 2151, Jonathan Archer, T'Pol, Trip Tucker, and Hoshi Sato were surgically modified to look like Akaali while they investigated a disease on their homeworld. Archer later discovered another false Akaali when he removed the prosthetics from a face of a Malurian agent. ()

In 2152, Malcolm Reed had cosmetic surgery to appear like a Suliban in an attempt to rescue Archer and Travis Mayweather from a Tandaran detention complex. ()

Later, Vulcan operatives Jossen and Menos were surgically altered to appear like inhabitants of Agaron. ()

23rd century 

In 2267, Captain James T. Kirk and Spock of the Federation starship  traveled back in time to 1930, and to explain Spock's alien appearance, claimed that a missionary had to use plastic surgery skills to save Spock's life after a mechanical rice picker accident, with the unfortunate side effect of pointing his ears. ()

In 2268, Arne Darvin, a Klingon Intelligence operative, was surgically altered to appear as a Human, but was identified during his mission to poison a shipment of quadrotriticale grain on Deep Space Station K-7. ().

Jadzia Dax also underwent a cosmetic operation to make her appear Human when, in 2373, the  went back in time to stop a future Darvin from tampering with the timeline. ()

Later in the same year, Thelev, an Orion agent, was cosmetically altered to appear Andorian, planning to sabotage the Babel Conference concerning Coridanite's attempt to join the Federation. ()

Still the same year,  Kirk underwent cosmetic surgery to appear as though he were a Romulan, in an attempt to steal a cloaking device from a Romulan battle cruiser. ()

24th century 
In 2346, during the Cardassian Occupation of Bajor, Kira Meru was brought to Terok Nor to serve as a comfort woman to the Cardassian officers. Gul Dukat, the prefect at the time, noticed a large scar on her cheek. However, instead of having her replaced, he used a dermal regenerator to remove the scar. () 

During the 2350s, a  assumed the identity of Starfleet officer Raymond Boone until his true identity was uncovered in 2370. ()

In 2366, Counselor Deanna Troi and Commander William T. Riker of the  posed as Mintakans while observing their primitive culture. ()

In 2367, Riker underwent cosmetic surgery giving him the appearance of a Malcorian. He then went undercover on Malcor III to determine if the planet was ready for first contact with the Federation. Unfortunately, he was captured, and upon examination, it was discovered that he was not a Malcorian. ()

In 2368, Captain Jean-Luc Picard and Lieutenant Commander Data underwent cosmetic surgery under the supervision of Doctor Beverly Crusher so that they could conduct an undercover operation on Romulus. ()

In 2369, Troi was kidnapped and surgically altered by the Romulan underground movement to assume the role of Major  of the Tal Shiar and help Vice-Proconsul M'ret and two of his aides defect to the Federation. ()

In the same year, Aamin Marritza, a Cardassian file clerk, had some cosmetic surgery to impersonate another Cardassian, Darhe'el, in an attempt to be punished for not opposing crimes committed during the Occupation of Bajor. ()

In 2370, Nikolai Rozhenko and his foster brother, Worf, were surgically altered to resemble Boraalans. ()

In the same year, junior officer Sito Jaxa volunteered for a mission which required her to be surgically altered to appear abused by Cardassian defector Joret Dal. ()

Jadzia Dax was temporarily modified to look Bajoran during The Circle's attack on Deep Space 9. ()

A bit later, Commander Riker and Doctor Crusher had cosmetic surgery to appear like Barkonians and uncovered what happened to Data after a Federation probe crash landed on the planet Barkon IV. ()

Riker posed as a Bajoran for a brief time in an attempt to root out a Maquis cell, but Ro Laren betrayed him and the Federation. ()

In 2371, Entek of the Obsidian Order captured Kira Nerys and altered her to appear to be Legate Tekeny Ghemor's daughter Iliana in order to expose Ghemor's ties to the Cardassian Underground. ()

Around the same time, Arissa, the alias of an Idanian Intelligence agent, underwent reconstructive surgery and her memories were replaced in order to infiltrate the Orion Syndicate. Two years later, Odo revealed her true identity. ()

Chakotay also was surgically altered in this year, in the Delta Quadrant, to look like a Vidiian in order to find out what happened to shipmates B'Elanna Torres and Tom Paris. ()

In 2372, Dr. Bashir erased the memory of Kurn, Worf's brother, and surgically altered his face so that he could assume a new identity as Noggra's son Rodek rather than be killed by Worf. ()

In 2373, a Starfleet team infiltrated the Klingon station Ty'Gokor in an attempt to expose Chancellor Gowron, the leader of the Klingon Empire, as a Changeling. The team was comprised of Worf, Benjamin Sisko, Miles O'Brien, and Odo. The latter three, not being Klingon, had to undergo cosmetic surgery. Upon arrival, they were captured when General Martok recognized Sisko. The team later realized that it was not Gowron, but Martok who had been replaced. ()

Later on, Neelix was cosmetically modified to look like a Ferengi, and portrayed himself to be the Grand Proxy in an attempt to convince Arridor and  to relinquish their hold on Takar II. ()

In 2374, Quark agreed to have his gender and appearance altered by Doctor Bashir to convince Nilva, chairman of Slug-o-Cola, that Ferengi females were intelligent and deserved certain rights in the Ferengi Bill of Opportunities. He was later changed back to a male. ()

In the same year, a pack of Hirogen ships successfully claimed the starship  and forced some of the crew to participate in vast holodeck hunting simulations. Certain personnel were surgically altered to appear like Klingons, including Neelix and Captain Kathryn Janeway. ()

In 2375, Damar arranged for Dukat to be surgically altered into a Bajoran. Under the false identity Anjohl Tennan, he gained the confidence of Kai Winn Adami in an attempt to free the Pah-wraiths from their prison. ()

Later that year, Neelix used a dermal regenerator to create a "pretty authentic" plasma burn on Seven of Nine to try and deceive the series 5 long-range tactical armor unit who suppressed The Doctor's programming and took control of his holomatrix. Neelix touted himself as the "chief cosmetics officer", to which Tom Paris said that maybe the captain would promote Neelix to "senior beautician". ()

In 2377, most of the stranded crew of Voyager was captured and brainwashed. The crew was then put to work on the planet Quarra to compensate for a labor shortage. The Doctor cosmetically altered the appearance of Chakotay so that he would be able to enter the planet without arising suspicion. Unfortunately, he was captured and identified while trying to rescue Torres, who was nearing the end of her pregnancy. ()

Other alterations 

Shapeshifter races usually had the ability to manipulate their entire physical state and appearance as they saw fit. These included Odo and other Changelings, races like Chameloids, Allasomorphs, and individuals like Garth of Izar. (; ; ; )

Around the same time, Cardassian forces genetically altered one of their operatives, Seska, to appear Bajoran and infiltrate the Maquis. ()

After Seven of Nine was torn from the Borg Collective in late 2373, The Doctor restored most of her Human biology and appearance, but she still had some visible Borg technology left behind. Further attempts to remove the last of her Borg implants proved hazardous to her health. ()

In 2376, The Doctor had his program modified so that he could appear like the inhabitants of a planet rotating 58 times per minute and determine if there was a way for Voyager to escape its orbit. ()  In 2378, The Doctor maintained the ability to copy the outer appearance of others by downloading their physical parameters into his holomatrix. ()

Later in the same year, The Doctor used medical techniques to begin transforming Ensign Lyndsay Ballard, who had been killed during an away mission and resurrected by the Kobali, back to Human form, including her hair. ()

In an alternate future, Data modified his hair to add a gray color to part of it in order to look older. ()

Cosmetic procedures and technologies 
 Colgonite astringent
 Dermal regenerator
 Dermal stimulator
 Dermatiraelian plastiscine
 Lobe enlargements
 Species reassignment protocol
 ChoH'a'
 Tooth sharpener

Memorable quotes 
(Referring to tribbles)
"They don't like you, Mr. Darvin! I wonder why? Bones?"
(Scans Darvin with tricorder)
"Heartbeat's all wrong... blood pressure is– Jim, this man is a Klingon!"
- Kirk and McCoy, discovering Darvin's true identity ()

"Be careful, android! Some Romulan beauty might take a liking to you! Lick that paint right off your ears."
- K'Vada, to Data, who is in Romulan disguise ()

"This is not going to work. It is not enough to look like a Klingon, one must act like one. Perhaps it would be better if I went by my..."

(Sisko backhands Worf across the face)
"Are you questioning the validity of my plan?!"
"Very convincing, Captain. But was it your intention to challenge me to a battle to the death?"
"No, not at all."
"Then next time do not strike me with the back of your hand. Use your fist."
- Worf and Benjamin Sisko, after their surgical operation ()

"The Doctor thought I should stick to my original [hair] color, but this seemed more exciting."
"Hair is one of my specialties, despite evidence to the contrary."
- Lyndsay Ballard and The Doctor, talking about her new hair ()

Apocrypha 

The comic book series Star Trek: Khan set in the alternate reality establishes that  was surgically altered by Section 31 after being discovered and given a new identity as John Harrison, explaining how his appearance differs from his Prime Timeline counterpart.

In the  novel The Good That Men Do, Trip Tucker underwent cosmetic and genetic surgery to appear as a Romulan for an undercover mission into Romulan space.

External link 

 

de:Plastische Chirurgie
fr:Chirurgie esthétique
Medical procedures