>>5900629you just need to take out the joint off the head, it can be hard but it's possible, if you manage to do it, loose the hole in the head a bit so the process can be easier next time you want to headswap.
for the thinker though you can take both samus' joint and head off, since the thinker has its own joint.
>>5900639maybe zero suit samus will have the same joint setup as the thinker, if she does, taking the helmet and the joint will do the work, if she has the same setup as snake's (peg on the head, ball peg on the neck, making the head jointless), as i said, you will have to take the joint off the helmet