Copyright law forbids the creation of derivative works (excepting any region-specific fair-use rules) so you're only allowed to create them under the rights granted to you in the terms of the license - thus under this particular license you can't make commercial use of derivative works.
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.