Guest adding a night to already paid booking

I'm wanting to offer my guests a discount for extending their stay, or coming in a day earlier, to help cover one night gaps in my calendar. How do I go about this exactly when they have already paid for their trip up front?

Thanks

Felicia 

Here are our general instructions for extending a stay:

https://www.ownerrez.com/support/articles/extending-a-stay

This process is very convoluted and appears to be far from "one size fits all".  Is it not possible to autogenerate a quote from your direct booking listing and auto-send that in a triggered message to provide the offer?  The only reason I can think of why one would care where the extension came from (i.e., from the originally booked platform or the direct-booking source) is that they would likely need to enter in their payment credentials on the new source (direct-booking) rather than it pulling automatically from the original source (such as Airbnb).

It would be simple enough to add in a better discount to extend through your direct-booking source, but still provide the option to extend via the original source.

Is this possible through OR, or through some third-party integration, or does this need to be a feature request?

Part of the issue here is the TOS'es of the various listing channels, that restrict or disallow extending bookings off-platform.  Since we have partnership agreements with the channels, we cannot intentionally design features to easily violate their policies, though there may be manual workarounds that we don't actively obstruct.

I’m able to update my reservation easily with Airbnb, but not booking.com. How would I do this with booking.com?

Here are our general instructions:

https://www.ownerrez.com/support/articles/extending-a-stay

Basically, changes to Booking.com bookings must be made on Booking.com, and not in OwnerRez.  You would need to check with Booking.com for specific instructions on how to do that on their platform.