What a convoluted and dumb way to make an incest patch.
I'm not an expert on reading code, but it seems like they wrote the script using hardcoded mom/aunt/etc, and if there is no patch, it does a word replace for those words and changes to landlady/etc. So the script is written with incest by default (mom/auntie/etc), but there is a code that replaces the incest words with landady stuff. And when you add the patch, it stops the word replacement from triggering.
Now, that wouldn't be a huge issue if the dev actually remembered to write the script using the incest relationship as the default, but starting from episode 2, he defaults to writing in the non-incest way. So the patch does nothing.