So the situation is let say character have transformative scythe. He attacks the enemy. Can then, his familiar that is capable of using magic items (and UMD) fly nearby, touch the scythe and spend standard action to change it into greatsword, then character attack with his new greatsword the next turn on his initiative?
I would say no, Only the wielder can activate an item. Otherwise anybody could walk by and trigger your wand of fireball while it's on your belt, just by saying the command word.
Any other thoughts? If the possessor is willing target?