G41 = Offset Left
G42 = Offset Right
It's not as simple as just adding them to the code. You also need to add lead in and lead out moves with them. Search this forum for G41/G42 and you should find lots of examples.
Personally, I think you'd be better off finding a CAM program that will do the offset correctly, or write proper G41/G42 g-code.
Adding G41/G42 to existing code can be tricky, and will get old very quickly.