I received an inquiry via DM about commission work with a character card from a backer's own, so I thought a post would be better than a personal response.
First of all, I had no plans to receive commissioned work.
Moreover, I can't even estimate the price for commission work. If I take on a request to work on it, please consider that it will take a considerable amount of time.
I am posting the questions you asked about because I think it would be good for others to refer to as well.
Q1. Is it possible to create the scene file I want?
Q2. When you want to change the character in the scene file on sale.
There is no need for me to do anything; It can simply 'replace' it using the mod in the purchased scene. It's not that hard.(maybe you can just change a few face part bonemods.)
BUT if you do 'Change', the bonemod values of the current character and the character you are trying to change are different, so there will be a lot of editing work.
In particular, differences in character's height can ruin a scene. This fix will take a very long time.

There are 3 character types used in my work.
I will post information about the character cards inserted into the project I am making over the weekend.
Thank you for your inquiry. If you have any questions about the scene you purchased, please send us a DM.