Routing signals in priority

I think you just add it to the project. Note that the .rcf does not dictate placement, i.e. you need to lock down all the logic in the path, and then the .rcf can route between the nodes after placement. If using TimeQuest, you can do report_timing with the -show_routing option to see the different routes between the one that makes timing and the one that does not. (Sounds like you're using the Classic though...)