Hmm, I wonder if you could just make the variable, then make it so complex to change it that it would be a waste of time to try.
Also, you said they'll just screw themselves over if they change it, make a warning that they shouldn't and then put some consequences if they do change it.
EDIT: Wait if i'm going about it right then can't you make the mod connect to a website then return the variable, thus making them not able to edit it?