I’m not in favor of any of those awful regulations, but it could be done pretty easy with laser engraving.
The point being that it would be REQUIRED on ALL magazines that they produce - even ones sold outside of Colorado. Thus the PMAG would get a reputation as being a traceable/registered magazine. This will cause them to be less favored in the marketplace.
Second, in addition the laser process would need to be added to the production line and before shipping. That would still be a costly re-engineering of their business processes. It would also expose them to a lawsuit if even one magazine gets shipped without the proper serial numbers and date of manufacture.