What if I can't just "try" it? What if the machine can only be used once? Or (my preference) if some deep "brain sex" transformation only works once, even if a more superficial motor remapping is easy to do or re-do? Come up with whatever frame story you want for this: maybe the machine costs my life savings just to rent for two minutes, or maybe the transformation process is ever-so-slightly imperfect, such that you can't re-transform someone who's already been transformed once, like a photocopy being a perfectly acceptable substitute for an original document, but photocopies-of-photocopies rapidly losing quality.
What if I can't just "try" it? What if the machine can only be used once? Or (my preference) if some deep "brain sex" transformation only works once, even if a more superficial motor remapping is easy to do or re-do? Come up with whatever frame story you want for this: maybe the machine costs my life savings just to rent for two minutes, or maybe the transformation process is ever-so-slightly imperfect, such that you can't re-transform someone who's already been transformed once, like a photocopy being a perfectly acceptable substitute for an original document, but photocopies-of-photocopies rapidly losing quality.