Legal in what sense?

People get different rooms than they booked all the time. Gosh, sometimes people even get "walked" to a different hotel than they booked. So that in itself doesn't seem illegal at all. Ie, if they had told you "sorry, we know you booked the king, but the queen is all that's available for the whole length of your stay, but you can check back next Someday to see if we can move you back into a king at that point" wouldn't that be legal? (A hotel may have had a guest extend a stay and now your reserved room is not available.)

So it is exact details of how they did it (them chanigng your actual reservation, rather than just putting you in a different room when you arrived) which is fishy. But if there's any "illegal" about it, it's contract law, and I bet the contract between you and Choice (regarding this stay) has precious few specifics about what your reservation really means. (I have a printout of a Chioce reservation from this week, and it says nothing about guaranteeiing a room type, just guarnateeing "my room" until 7 am with the credit card. But again, "my room" can include being "walked" to another hotel, so it's nowhere near as specific as the exact room that's listed on the reservation.)

So the only thing I find potentially "illegal" is the fact that they lied to Choice Customer Service about this. That doesn't involve you directly, that's between the hotel and Choice corporate. (You're just a "witness", in a sense, in that potential illegality!)

What they did to you is "nasty", "not customer friendly", etc, but I'm not sure on what exact basis it could be found to be "illegal".