Bootmode on a bench harness will let you read and write your ECU.
Then you just need a stock file to modify to your liking
No need to immo off.
But you could buy a spare ecu to make your own tune on,
And keep your old one as a working backup.
You can always match your ECU to your cluster, and vise versa.
But AFAIK key transponders can only be written once.
A good starting point would be to post your ECU HW# and SW#