Alright, I have made progress.
I've managed to find out what ActivateStuff uses as its only variable, borrow some raycasting script from an activation event (OnAltActivate, OnFirstActivate, OnRapidActivate) and find the typemask for player objects.
(And making taggers freeze and untaggers unfreeze, of course.)
I will proceed with a temporary multiplayer test, of course.
All that's left to add is making an ice block around frozen players or changing their appearance so that every body part and cosmetic gets colored Cyan. Though I don't know how to do either - Can anyone help me on this?