ribbot,
I booked Pop Century at rack rate last week and unless things have changed, this is how expect things to go:
In a few days/weeks codes for my time frame (Jan 1 - 10) will come out. In the past I would call CRO and book my room under that code's rate, then cancel the old ressie which carries a higher rate. Some folks here say you can just call Disney, have them pull up your ressie and apply the new, lower code rate to what you have. In my case, I'm probably going to trade up to a moderate so I'll just cancel the old and book the new. The one night's deposit on tha old ressie gets applied to the new.
You can't use multiple codes on one ressie, if that's what you're asking, at least not by experience. Codes have dates that they are good for. A code for Jan 1 through Feb. 15 would be no good for April, you'll have to await the April codes.
Bill From PA