OK thanks, so just the standard change rules, other than you didn't incur a reservation fee in the first place.
A reason I asked this is another question I have, namely about point buckets.
Lets say you owned at W57th, and reserved a 2 day 1 BR stay during the resort window with your bHC points, and then exactly 60 days till the start of your reservation, you see availability immediately before your 2 day stay (for example, 2 days before the start of your current reservation), could you change your reservation to add the 2 days using your HGVC points, since the 2 days are now in the club window (<=59 days)?
In the attached picture, assume the 2 days circled in blue were the ones you already reserved, and the 2 days before are the ones you want to add.