I want to backdate a contract change but am worried that this may have a knock on effect. Posted on May 28, 2009January 3, 2018 by Matthew.Evans If you backdate a contract it will affect FMS. If you have reconciled against the old contract, we would suggest to not backdate unless you are happy to change FMS as well. Reviewed 03/01/2018 kb112 How useful was this article? Click on a star to rate it! Submit Rating Average rating / 5. Vote count: No votes so far! Be the first to rate this post. Posted in Personnel and tagged backdate, contract, FMS.