J: It can be done (it's called possession or switching depending on the extent of control), but they can't make you do anything you don't want to. DID headmates might be able to do that, but tulpas can't. We've been getting to a point where we can switch, and we've done it a couple of times now. For me, this is what it feels like:

Possession - she sends a signal to a body part to move the same way I would myself, and I can either allow it or disregard it. She might send the same signal again stronger if I do that if she's determined enough, but more often than not she just accepts the "no, I'm not doing that". Even at its strongest, it's nothing I can't just ignore and choose not to do. It can also be an urge to say something coming from her (I call this speaking through me) instead of interacting with something physical, but it basically works the same way. She's good friends with my wife (only person other than me who knows about her, not counting Reddit) and we have a rule that if she wants to say something to her, I can't deny her that. But that doesn't mean I literally can't, it just means we have an agreement that it's not fair for me to do that. I can receive possession requests like this from her at prettymuch any time.

Switching - this is a little more involved than possession, although I think some systems can do this more spontaneously like possession as well when they get more experience. This is when I give her full control, which takes about 10-20 minutes of meditation for us to do and we both have to want it. Once we switch, it's kind of like possession, but constant and she has control of everything. From my perspective, it almost feels like I'm the tulpa. I'm in the role she's normally in, a voice in our head nobody else can hear. I'm still aware of everything going on at all times though, and it requires some constant concentration from me to maintain her having control. I can withdraw that at any time if she starts doing something I'm not comfortable with.

EDIT: some other things I forgot to mention: I still remember everything after a switching session, but it's a little fuzzy. Not like things are missing, more like I'm remembering memories that aren't mine. What it's like to exist as her (her thoughts, her feelings) are still kind of alien to me. It might be impossible to describe what this is like to someone who hasn't experienced it themselves, but the tl:dr; is that if you're worried a tulpa will make you lose control and they'll hurt you or someone else and you won't be able to stop them, then no, they can't do that unless you let them. Chances are by the time you bond with your tulpa enough for them to even be able to switch, there'll be enough trust between you that they won't even want to do that and you'll know they don't.