concerning pretend play

Ds#1, now 3.5 years old, is going through a phase where he is almost never "his real name" (the concerning part) but instead any one of a number of other individuals or entities, usually cycling from one to the other several times throughout the day. At times I get it; he'll pretend he is his playdate buddy whose mother is carrying a bag of goodies that he wants that day (so that he can claim the bag is really his posession, being the mother's "child"). He'll also become someone or something else to escape responsibility. Other itmes, he's just pretending he's a bat for the day so he can flap around and squeak and eat mosquitoes. Just for the hell of it. But I wonder if I am going along with too much of this, because I wind up reinforcing his play and letting him act out all of these fantasies.

Is there good literature on this topic, or can anyone comment on this? I'm googling "pretend play" but I need to know what to call this phase. Is it "out-of-control pretend play?"