I changed resorts from ASMu to POFQ and added a day to our stay at POFQ. I didn't have any problem making changes, but i am still 60+ days out.
Both times i made changes i had to do it differently. To change resorts, I had to book POFQ online and then call and cxl ASMu. To add a day to POFQ, I just had to call CRO and add a day on. I still got the same BRP rate and didn't have to pay another deposit or any difference.