I had a guest that booked for 6 weeks, and 5 weeks into his stay wanted to extend for another week. This was last August, and I was unable to use the change reservation function to make this change (because the arrival date was already past). I think he had to create a new request, and then I responded with a special offer that gave him the monthly discount. But it didn't bill an additional security deposit (or maybe I was able to change that too). It wasn't as elegant as I would have liked it to be.
Now I have another guest asking about the possibility of extending his stay. If he makes that decision before arriving, the change reservation function is fine. Is there a better way to do it if he decides after arriving?