I know this is a total Noob question but here goes. I want to purchase a “spare “ ECU to practice on so I don’t brick the one in my car while learning. What do the letters refer to at the end of the part number. Specificity an ME 7.5.5 . My car has a 8N0 906 018 K can I flash the map from it to a 8N0 906 018 L for instance. Is they letter just what program is in there? My assumption is as long as the base part number is the same the letter is just a mod to the program. There are allot of used ECU’s out there and the prices very allot. So trying to figure out if I can buy a S,L,AN or whatever and reflash it with no problem.
Is there a reference somewhere the shows what the different letters refer to.
Thanks in advance.

In general assume that ecus cannot be cross flashed unless known to work. There are threads on here that list known good combinations.