Previously it has not been possible to drop down from the WSL into the third tier, the Women's Premier League (WPL).
The league have also revealed that applications for WSL licences from 2018-19 will initially only be open to the existing WSL clubs, not new teams.
But should any club fail to meet the criteria, then other clubs may apply.
Meanwhile, WSL clubs are to receive an increase in funding from the Football Association, up by as much as 79% for second-tier sides, as follows:
There will be one relegation spot in WSL 2 from the end of the first winter season to drop out of the WSL.
One club will continue to be promoted from the WPL up to the second tier, via a play-off, each season, with the winners of the WPL Northern Division facing the Southern champions.
In between WSL 1 and WSL 2, one team will continue to be relegated each season, while one team will be promoted.
This one-up, one-down system throughout the top three tiers means there will a total of 20 teams in the WSL, with 10 teams in each division, bringing a halt to the WSL's expansion, which started in 2014.
These changes do not apply to the 2017 Spring Series - a one-off, transitional competition where there will be no promotion or relegation, while the WSL switches to the winter calendar.
With an initially closed process for licence applications, the existing WSL clubs - plus those promoted to WSL 2 by right - will have priority over any new teams wishing to join the league.
This reduces the likelihood of new women's clubs joining the WSL without working their way through the lower divisions of the women's football pyramid.
But should any WSL club fail to meet the criteria for renewal, in any future season, then the door could be open for a club that does not currently have a top-level women's side to enter.
Relegation from Women's Super League Two will be introduced for the first time in the 2017-18 season when the WSL adopts a winter calendar.