The umakerc file is normally only used for debugging and is parsed by umake every for every invocation of umake. It is parsed after everything else and can thus change any setting in any umake file. Needless to say, this file should be used with caution. In order to find your umakerc file, umake looks in the following places:
The umakerc file has the same syntax as a umakefil, but the only function which is really useful is project.AddDebugOutput.