When was the annointing performed?
Ramban #1 (citing Ibn Ezra): It must have taken place before Moshe placed the Mitznefes on Aharon's head, because once the Mitznefes was in place, how could he pour oil on his head. 1
Ramban #2: It took place after the Mitznefes was in place. 2
How was it performed?
Ramban: The turban was wound round the outseide of Aharon's head, and Moshe poured the oil in the space on top.