You can't transfer points from one home resort to another.
I have 200 points for SSR and 200 for AKV (both February). If I want to book SSR at 11 months and need more than 200 points, I have to bank or borrow from my SSR points.
At 7 months, I can use all 400 points anywhere.
So let's say I want a week in a THV in Magic season. That's 315 points. Since they go fast, I need to book at 11 months. I use all of my current 200 SSR points plus borrow 115 points fro my next SSR UY. My AKV points are untouched.
Keep in mind those those borrowed points can never go back to their original use year.
Let's say instead of that I decided a 2BR at SSR is fine, so I don't book anything until 7 months. Then I could book 2 ways (and do tell MS which way you want). I could book the same way I did, borrowing 115 SSR points (or for that matter borrowing 115 AKV points - I might do this if I know I want to preserve the other resort's points for another reservation at greater than 7 months) or I could use a combination of SSR and AKV points to book. You can specify how this is split - I think if you don't say anything, they would book with 200 SSR and 115 AKV from your current UY.
Hope that helps!