Not everyone qualifies to bypass the desk, and not everyone does online check in. I have only asked to change rooms once since the bypass the desk program started, and I didn't have a problem doing it. I was in a very noisy location and asked to be moved to a quieter one. I would think there would be some inventory available to swap out, but no guarantee it would be renovated rooms.
For what it's worth, on the days I check in, I do online check in with an estimated arrival time of 2pm so I can have a good chance of getting the room assignment before I leave work for the day. I usually arrive around 4:30, and if I put that as my estimated arrival time, sometimes the email comes after that time (sometimes after I've already gone to the desk because I didn't get the email). My last three stays I did get a renovated room. I do make that my only request, and really don't care which building I'm in or what floor I am on so long as I get a renovated room. The arrival time in the online check in is only an estimate anyway, so if your plane is arriving very late, I would put in an earlier arrival time so you can get your room assignment and know in advance whether you will need to make a change or not.