Let's say I buy a set of plans for scratch building and decide to make the wings longer or the cockpit wider. Let's also say that I 'ran the numbers' and am confident that the changes are safe.
Or, even more extreme, I buy plans for two different aircraft and use the fuselage from one and the wings from the other.
Am I free to make the changes I want as long as I change the model designation on the paperwork so that the designer(s) safety record isn't put at risk? How much ownership does the designer retain regarding what I build and how I use it beyond the restriction to only build one primary unit of any part.
Dave