I think you can use the code to book all of the rooms; however, if it's your code, you have to do the booking. Verify this to be sure, but when we called to make our reservation using our 40% code, the CM told me I could book additional rooms using that code (at the time, my brother and his family were thinking of going to WDW with us, but changed their plans). Since I didn't do it, I can't say for sure that it's allowed. But, it's definitely worth asking about. Good luck!