I just did this swap on my 2012 A4 Avant.

The OP's instructions were excellent and took me about an hour, including putting the old wheel back together.

I would have finished in about 30 minutes, but I was swapping in a B8.5 flat-bottom wheel with the airbag that has the spring-loaded clips instead of the T30 screws and it was already inserted into the wheel when I received. This made it extremely difficult to get the new airbag out single-handedly so I could install the new wheel. Fortunately, a friend was nearby to help and we were able to get out with some coordinated effort.

If you receive a wheel with the spring-loaded airbag pre-installed, I would highly recommend having a friend assist getting the airbag out before beginning the swap.