Since it's an aluminum frame, the 'braze-on' is either epoxied or riveted on.

If it's riveted, you can just drill out the rivet. Pretty simple.

If it's epoxied, I would go with a file, and be very, very careful. It won't take you forever, 15 mins per guide tops. Don't use a power tool because one slip of something like that and you'll be tearing through your coke can.