No permission is needed from hospital diabetes specialist nurses, but there is no harm telling them.
About three years ago I mentioned to my diabetes nurse that I was thinking of self-funding Dexcom. Although it had been made quite clear that I would have to self-fund, the nurse arranged for a Dexcom rep. to meet me at the hospital, to show me the correct way of inserting the sensor. I seem to remember that the rep. had a dummy sensor for me to practise with.
Later on, I changed to self-funding Freestyle Libre, to save money A year after that NHS started funding the Libre.