question about applying discounts

[disneynewbee]

I just got a discount code from disney destinations for 40% off of a standard room at a value. If I call and book with this discount can I call back later when the discounts come out to the disney visa members or general public if that is a better deal and change it? Also is the disney visa general public discount usually better than this 40%? We got the discount on our last two trips and I'm pretty sure it was a better deal but I can't remember 100%. TIA