Unfortunately I don’t think it would work as simply as that. That’s not a runtime config file, it’s a C++ source code file, so at the very least you’d have to rebuild the application yourself with your modified source code.
Even after doing that, I’m not sure if just changing false to true is enough there. (If nothing has changed since the earlier post from Feb 2025, then it wouldn’t be enough.) But that’s not very informative since I don’t really know anything about the internals of kdenlive.