It’s hard to have CGs with character changes like that. If the CGs were more uniform in their presentation, this would be easier to do. Maybe in a future game. I can’t see doing it in Succubus Stories with the amount of work it would end up being.
Yeeh, that makes sense!
I do have one alternative suggestion, in case that would be easier; If the succubus herself can't get pregnant, perhaps you can include pregnant NPC characters? Needing only images for that specific character should make it much easier, unless I'm misunderstanding how it works
Either way, no stress!