We already don't actually lock rosters until we go to print the paperwork, so you should have some window in there no matter what.
But I'm not sure how that's going to help you. Can't split the games into two sessions without giving people back-to-backs, and the 10-man field will be closer to the UWL fields than the RaceTo field, so there's pretty much no circumstance where you won't have at least one case where it won't be possible to get from RaceTo to 10-man and back again (or vice versa).
If you just have guys playing on more than one RaceTo team and you just don't want those overlapping, email firstname.lastname@example.org
and I'll see what we can do when we're making the schedule.