[dec0dedab0de]

But is a physical item a derivative work of it's technical specifications?

If the design files qualify for copyright protections, then modifications to them would clearly be derivative works.

I don't think it is clear if the keyboard itself would be a derivative work, as it almost certainly can't be protected by copyright. This is what patents are for.

[thereisnospork]

Ianal, usual disclaimers, etc.

The design files don't qualify for copyright protections, they describe the design which (maybe) qualifies for copyright protections.[0]

The artistic design of a specific keyboard can certainly be copyrighted, but not the functional nature of it.

[0]The exact wording might be protected, but not the factual information contained. Sports scores, or say measurements of a keyboard, are not copyrightable items as they are just facts, though their presentation might be.