Replacing code whose license you don't want is definitely a fair-and-square way to manage a project and change the overall terms under which you can distribute it. (As it happens, that tactic is often essential to efforts to open-source formerly proprietary projects, too.)

*Provided that the replacement is not simply a rewritten version of the same code that achieves the same result through overwhelmingly similar methodology.

The function of code is explicitly not protected by copyright and the breadth of this exemption was clarified and expanded by Google vs Oracle.