I think from what I've read it basically replaces your entire personality so you aren't so much forced to act a certain way against your will as that is what you do naturally. Think of someone you know and then imagine that personality in your body. How they talk, walk, what foods they like etc. Your still you but your a different you. For example say you were a guy really looking forward to an upcoming sports game and we uploaded a basic female personality you'd still be looking forward to the game but all the things you do e.g. walking, inflection when talking, crossing your legs when sitting would match the female personality uploaded and you wouldnt notice them as theyre natural.
To take it a step further a few treatments, a more complete persona fix and bam you look like arnold schwartzenigger, sound like him and think you are him. Except instead of going into politics your happy to make whatever paid for time with you feel like your world revolves aroind her, till time runs out.
Its why their so dangerous kidnap someone off the street, install a persona-fix and their goals and dreams are replaced by a desire to serve you even if theyre still the same person otherwise and theyll sign whatever you want with a signature indistinguishable from what they used before then legally you can do whatever you want to your new enployee because they signed the contract.