That would be an interesting headache. I would hope there are some sort of back end checks in place for this type of modification
I once heard a story about a store-clerk who, upon finding their POS setup was broken, went down the street and 'borrowed' a configuration file from another store in the area that they happened to know had the same software.
Blissful in their ignorance of what was going on they then happily continued accepting transactions for the rest of the day. Oops.