Hi! A software update should be a total update and not just the transmission/Idrive. I had a complete update and my car was 2 years out of warranty and not covered, There are some risks in doing the update but if you have a CPO you should be covered.
There is a transmission update which really smooths out the transmission, but as I said it cannot be done separately, (unless my dealer was a little lie teller Lol)
Always said I would go back to a 6 series