It does seem like it should be easy, but here's why it doesn't work that way. Let's say you booked a 2BR AKV CL at 8am when your 11 month window opened. Now, let's say I tried to book a 1BR AKV CL 5 minutes later but it wasn't available and I had to waitlist it. Fast-Forward 7 months...it is now four months before travel date and my waitlist still hasn't filled but now you decide you only want a 1BR instead of your 2BR. There are no 1BR's available so you would need to join the waitlist. Just because you had a 2BR booked does not allow you to "jump the line" for a 1BR. Your cancelled 2BR *might* be converted into a 1BR and studio and thereby fill someone's waitlist, but it also might remain a 2BR...we don't know. Since you now want a 1BR instead of a 2BR, you have to get in line behind the folks that wanted a 1BR 7 months ago.
I understand and sympathize with your train of thought. We often travel with my parents and they cannot always commit at 11 months. Since we have a small contract, it is not possible for us to book a 1BR and a studio. When the parents come along, we have to really stretch our points by booking a 2BR. Although they have never had to cancel yet, it would be a huge blow to our points if we were "stuck" with a 2BR for the 4 of us, but that's what we would do.