Can I add new characters to currently saved game mid way through the game? I have a char that is a vamp and I want to add a new char to replace him.

If you have empty slots in the Inn, you can just make new characters whenever you want (until it is full). Each Inn is different, so if you made a character in Valeia, they won't be available in Ishad'Nha unless you physically move them there with the party. Just leave the old character behind or delete it. This is also useful for re-initializing stuck quests, lamp uses, etc.