I JUST did this with my AKV add on. My situation:
I had a reservation in december at BLT that used the remainder of my 225 June 2010 UY points, and I had to borrow 26 points from my June 2011 UY. The plan was to switch that BLT reservation to an AKV reservation in december, when my 7 month window opened up and bank the excess 2010 points back in to 2011.
However, after some more playing with
point charts, I found that I wouldn't have enough points for what I wanted to do in 2011... and would be borrowing even more points... so I determined I didn't own enough points... Time for an ADD ON! (they really need a prescription you can get for the addonitis...they can call it addonitol

)
The reservation I wanted at AKV was 87 points and I needed those points in my June 2010 use year... the current promo is that you get 2009 points too with an addon... So I did an add-on of 60 points... this gave me June 2009 points which I banked in to June 2010... to give me 120 AKV points in June 2010. I made my reservation, which freed up 96 BLT points, including the 26 that I borrowed. So now after i've switched my reservation, I have 33 2010 AKV points, 70 2010 BLT points, and 26 2011 BLT points in my June 2010 use year.
I specifically asked my guide about my 26 2011 BLT points that I borrowed, before I did the add on, and he said that if you do an add on to pay for existing reservations, they will let you do just about anything you want...swap points on the reservation without having to cancel and rebook, unbank, unborrow...whatever.
I didn't have any problem, and they put them right back. Just make sure you clear it with your guide first...but he seemed to suggest it's a frequent request regarding add ons.
I now have my full 225 point allotment of BLT points back in my June 2011 use year, as if they hadn't been borrowed at all.
And now I have 70 2010 BLT points, and 33 2010 AKV points to bank in to 2011
