Default Preventing app writing to xml

Hi, I have an app that allows downloads however, after 2 downloads, I'm required to click on an ad for a few seconds to allow more downloads. I've managed to stop the ads but want to get rid of the ad click action. I've traced it to a small xml file that simply increase a value="2". Can I simply stop the app writing to this file and will that work? I've tried changing owner and permissions but the app just changes them back on run. Thanks