In theory, you're right, but my opinion is that in reality, it's very difficult to execute. A good story about a forbidden romance is not just a few scenes here and there with comments like "I shouldn't be doing this". You have to see the character in conflict, in their actions, and their thoughts.
I'm not sure I've made myself clear, so I'll use an example. Let's take Romeo and Juliet. Now imagine that because of the social norm of this time, Shakespeare had to create a patch to change the relationship between the two main characters (people underestimate the historical influence of Patreon lol). In my opinion, it wouldn't work, the forbidden romance is so central that he would have to write two different stories, or one of them wouldn't make sense. I feel it's the same with a good incest story. The few very good I have in mind wouldn't have worked with a patch, I'm sure of it.