CAN YOU CUT A 2 HOLE LUG DOWN TO 1 HOLE?

You can, but you will destroy the lugs certification if you do. Without the certification on a field modified piece of equipment you stand the chance of getting a rejection if the project is ever inspected by an electrical inspector.

Just use the double barrel lug until you can get a proper single barrel lug and then change it out. Keep in mind the cost of a double barrel lug is about four times that of a single barrelled lug.