I'm sure that the work-around topic came up many times, but I could't get the correct key words in order to search for my question, my apologies.
Did one light Color grading on material, did a round trip FCP render and added the XML for final grading.
Is there a way I can get the XML shots flat again with out any grading and CC the XML footage from the scratch ?
That is doable. Did you keep the same filenames when you rendered the one-light stuff?
Try a Reconform from Folders. Import your XML and have it bring in the one-light footage. Then in your media pool, create a new folder under ROOT and import your original footage inside this new folder. Then right-click in the Resolve timeline and choose "Reconform from Folders." See page 150 of the Resolve manual.