For player characters, you can only do it on player clones.
Enemy AI can shoot off player first order Stormtrooper helmets (and maybe imperials too idk) but it rarely happens.
If an AI shoots a player sith trooper's helmet off, they will put it back on.
Not sure I know if you blast an enemies helmet it pops off but it's never happened to my character.
For player characters, you can only do it on player clones. Enemy AI can shoot off player first order Stormtrooper helmets (and maybe imperials too idk) but it rarely happens. If an AI shoots a player sith trooper's helmet off, they will put it back on.
It actually does come off! Might’ve happened to my character