No, borrowing is final and moves the points into the previous UY where they stay. You then have to use them or they will expire before the end of that UY. If you also have used current points on the reservation then MS should use all the borrowed points first for the new reservation and then whatever current points would be required leaving the remainder of current points to be banked if you are still in the banking deadline and if the change occurs more than 31 days ahead of check in. But if you've borrowed all the points for the current reservation and the waitlist is for less then you would need to have a plan to use the points before the end of the UY if the waitlist filled.