The pair will take charge of the Welsh Premier League champions for their forthcoming Champions League campaign.
TNS owner Mike Harris hopes Ruscoe and Evans will be permanent replacements, but says one of them must complete their coaching qualifications.
"Scott or Steve will have to find a Pro Licence course somewhere," Harris said.
The Uefa Professional Licence is a mandatory qualification for anyone wishing to manage a football club in national leagues within Europe.
"We're hoping the FAW [Football Association of Wales] may have another course to run and they get selected for it," Harris added.
"If they don't we'll have to find someone else around Europe, because one of the things the club prides itself on is our succession planning.
"Scott and Steve Evans have been in situ for two to three seasons so that as and when that day came [Harrison left], the club wasn't having to scrabble around trying to find someone in an emergency."
Harris revealed that he has had plenty of applications from outside the club for the vacant manager's post, but for the moment is happy to give Ruscoe and Evans their chance.
Coaches Scott Ruscoe and Steve Evans have been put in interim charge of The New Saints after manager Craig Harrison left to take over Hartlepool United.