I am a design engineer, and I sometimes take some reference designs and replace some sections with our own customized designs. I need a single word to indicate the "our own design". Something like Legendary design. I need to say it as "design completed and xxx section replaced with legendary (for example) design.
I'm not entirely sure I understand your point, but "proprietary" is commonly used in the automobile industry for these contexts. For example, a shock absorber is a part used on every automobile, but every company which is in the business of manufacturing shock absorbers takes inputs from the automobile manufacturer and gives them a specially designed "proprietary" part.