> any legal requirement is published and available freely
Hmmm..... For house-wiring, the only legal requirement is Town Building Code. However many towns adopt a State suggested code. And nearly all local electric codes adopt the NEC in its entirety, then overlay local differences. (Here the only difference is that the 2006 NEC is still the law of the land-- we don't fancy the wizzy-wonk changes in later NECs.)
At least NEC is readily available for the price of a college text-book. (Favor the NFPA edition with annotations.) Back-years of NEC go slightly cheaper on eBay (which may be part of our local preference).
As for UL (inside your box).... the books are very expensive, sub-divided, you might need several volumes. The actual Testing is VERY expensive, tens of thousands of dollars.
If your house burns down, and non-UL gear is found in the ashes, this is legally legal BUT your fire insurance policy may balk at paying-off. UL is "Underwriters", a fancy name for insurance, and the origin of UL.
You probably can not sell to Guitar Center etc unless you show UL testing. (Retailer fear of non-UL stuff is why we see very little non-UL on the market.)
But if it comes to court, having a UL tag does not make you loss-proof. These cases often come down to who has the bigger lawyer. Between broke musicians and broke boutique builders, I suspect lawyers rarely get into the fray. Even if "you killed somebody", most lawyers would look at your chicken-shed "factory" and 2003 Kia "company limo" and decline the case.
I do not think it is prohibited to use Green generally, just at the Power Entrance where only the Ground can be Green (Green/Yellow).
I don't think using a green wire saves your ass. The real point of these provisions is that when you rip the power cord out, the ground is the LAST to break, and no incidental damage happens when it breaks (it has a dedicated screw). The IEC connector is preferable to a grommet, because it will break-away without any damage.