The spell switcheroo is overpowered, IMO. It would be far too easy for an imprisoned mage to lure a guard over to their cell door, cast this spell, & just walk away while the guard is stuck on the wrong side of the bars. As written, even a rat (a ubiquitous fixture of fantasy-genre prisons) would suffice, turning what is normally a creature that is merely flavor-text-fodder in most stories into an ad hoc jail key. And this is just one scenario usable by a 1st level mage.