The developer could create the ability via the Safari share sheet. Click on an ad, and the share sheet for the app comes up. Click on the app and then you are offered certain options as to how to handle video, text, fonts, ads etc. And depending on which option you chose, it would then send the new rule to the correct section of the app.
In regards to the aforementioned, users need to be able to back up their custom rules. A developer can create the in app option to save the app rule package to the computer, Dropbox, OneDrive, GoogleDrive for safe keeping. Automatic backup of custom rules. That way, if a user needs to reinstall the app, he or she can easily input the custom user rules list into the app.