Weight loss of any kind can jeopardize the coming season, and no weight gain won't help either obviously.

IF I were to try switching them I'd wait till after the breeding season.
I say "if" because I only feed live but I breed and can, some can't.

More info would help.
Age and weight of females especially.

When I fed F/T to some snakes I always had a back up live rat in case the snake didn't eat the F/T.
I waited till the following day to offer the live rat then the next week I tried the same routine till the snake took F/T.