Hello
See the "Revert member" feature. but I am not sure if it is without creating a branch.
Practically if I have to do so without wanting a branch, I get the older revision and overwrite/check-it in over head revision to revert manually.
To get an older revision:
you can make a checkout or better a projectco if you don't have a sandbox with as option the revision you want.
See discussion http://communities.ptc.com/message/251245#251245
HTH
Thierry