Recently bought a XXL550TM. After reading up on model differences, I would like a 540TM. My son has a 540TM. I have done backups for both units on my computer. I was wondering if I were to delete the 550 software from my unit and load the 540 software onto my unit, what problems might I have? Will it work? What about the activation code for lifetime maps that I had already activated on my 550?