Copyleft licenses, at least when Conservancy enforces them, are definitely non-negotiable: https://sfconservancy.org/copyleft-compliance/principles.html https:

Copyleft licenses, at least when Conservancy enforces them, are definitely non-negotiable: https://sfconservancy.org/copyleft-compliance/principles.html https://sfconservancy.org/copyleft-compliance/principles.htm... "Our primary goal in GPL enforcement is to bring about GPL compliance. Copyleft's overarching policy goal is to make respect of users' freedoms the norm. The GNU GPL's text is designed towards this end. Copyleft enforcement done in this spirit focuses on stopping incorrect distribution, encouraging corrected distribution, and addressing damage done to the community and users by the past violation. Addressing past damage often includes steps to notify those who have already received the software how they can also obtain its source code, and to explain the scope of their related rights. No other ancillary goals should supersede full compliance with the GPL and respect for users' freedoms to copy, share, modify and redistribute the software."