I agree with Granny. "impossible" isn't the right word, but I sure wouldn't count on it.
Book your home resort at 11 months and then try for a day-by-day swap (or waitlist) at 7 months.
Last year, we ended up learning in the week before christmas that we were going to have a week in which we could travel just after new years.
I made my first phone call looking for lodging on Dec. 22nd and managed to get ASMusic (for cash) for Dec. 31st, BCV for Jan 1&2, and SSR for Jan 3&4.
Sure, we stayed at 3 resorts in only 5 days. But, we only spent one really long day (8 am to 2 am) in the parks, so, the different resorts gave us more easy areas to explore.