@Wiredcat Robotics @kypro
The question at this point is if you can even tell if it was bought from the store or, to say it this way, "home-made". I don't agree with making your own stuff (with similar reasons as you've said) but if it's so similar, but if it's done well enough there's a chance an inspector wouldn't even be able to tell. I've never made any of my own steel/aluminum c-channels but on the VEX Store it tells you what finish they have and what material they are made of, and other things like hole size, thickness, and after a bit of a second look you would know that the center of each hole is half an inch away from each other.
If you show up at one of our tournaments with your own shop-built VEX structural parts, you'll very likely be turned away. We've had metallurgists, precision sheet metal designers, and metal finishing experts among our officials.
Beyond that, it would be very difficult to duplicate the look, fit, and finish of VEX parts with CNC. The differences between similar but not identical parts is usually quite stark. Tiny differences in metal composition and processing will make big differences in overall look.
In the end, its a try-at-your-own-risk sort of thing.
No, in the end it's against the rules to make your own parts. It's even against the rules to subject VEX metal parts to processes meant to modify their properties, like hardening or tempering. This is both so that teams can't gain an advantage from special processing, and for safety. Having a brittle metal part catastrophically fail in a competition would be a bad thing, so REC gets to make the rules.