The challenge is, RTD/src/Det.c is generated code, and I'm not sure the peripheral configuration tool lets us turn this one off. So even if I edit the function as you suggest, it would get overwritten the next time peripheral configuration changes and code gets generated again. It isn't a __weak__ function either so I can't just replace it with my own function of the same name.
I ended up using GCC linker's --wrap option so, any calls to Det_ReportError go to my own implementation named __wrap_Det_ReportError.