Well, could they be forced to be something they don't want to be? Assuming that these are tuppers and not just puppets, I could see it going a few ways.
Some people might claim that they can control everything about the tupper whether or not they like it. That they can change their personality in a second or something. While I would say that if this actually happens, it's not a truly independant and sapient tupper like we would require them to be for them to be "real" tuppers... I guess there's the possibility that the host and tupper think this can happen, so it does happen. Considering that everything happens inside their heads, that stuff can be easily manipulated if they don't realize that it can be stopped. There could even be some symbolism that the host and tupper believe in so much that it overrides the tupper's own free will or powers. I guess it could also happen to a host and a host could be molded in the same way, but it's going to require a pretty strange mindset for it to work. A mindset that might be impossible to achieve unless we're looking at a really submissive personality that thinks the one "controlling" them is much more powerful than them and able to do anything they want. They would basically have to give up and give in, not resisting in any way. Not many conscious beings would want to do that, I think.
Or that it just plain isn't possible because a tupper has such a strong will and is able to resist what you try to force them into because they don't want to do it. The more confident a tupper is of their own abilities, the harder it would be to force them into something they don't want. If you have managed to create a tupper that is truly independent strong tupper that needs no host, you're not going to be able to force them into something they absolutely do not want to do. Assuming you don't pull some shit out of your ass that fools them into thinking you can suddenly override their will, of course. Or they somehow agree to it, which might or might not take hold and would most likely change eventually, as an actual person will never stay the same. If you remove their ability to learn and change, I'd say you remove their personhood - and that way also their tupper status as they no longer seem exactly sapient or "realistic". Again, not something I would see happening to an actual tupper unless they have a fucked up mindset.
Some actual "forcing" might happen during personality and form forcing, as you create a personality and a form which they are then "forced" to use. But honestly, I'm not sure how much of it would affect them if they decide they want to do something else instead. A forced personality would be a rather simple one in the start anyways and they would only truly mature and grow into their own person through experiences and time. It's something you can't force and even if you do personality forcing, you are going to end up with something that had grown to be what they are now, not something that you forced to act the way it does.
Unless you are actually forcing it to act the way it does because it's a puppet. What do I know.
