When there is a robots.txt in file system

I found if these is a true robots.txt in the file system, then this module doesn't work. Is it possible to add an option for it ? When there are 2 robots.txt, users can choose they want to use the file or the module.

If this solution is not a good idea, maybe you can consider to add a reminder, when the file is existed, show a warning to users that this module doesn't work, thanks.