Yes, the TEC-9 was easily convertible to be full-auto. No, it should not warrant the submachine gun tag (which should be given to the Interdynamic MP-9). If anything, it would probably be closer to a machine pistol but the TEC-9 was intended to be a semi-auto pistol anyways.

This weapon's a pain in the butt to tag. But for now, the SMG tag is coming off.