if the hardware PN is the same, dump your original ECU and write it to the spare with immobilizer disabled
if you need someone to turn off the immo, let me know. i can do it for you, just PM me and ill send my email if you want to do that
hell, even if the spare ECU isnt the same PN as your original, i'd flash it anyways to test LOL
you really cannot brick the ECU when you have access to the boot pin AND the original dump that was loaded. so make sure to READ both ECU's and store those original reads somewhere safe!!!!!!!!!!
edit: just remembered you dont have a TDI..... ill still try to immo off your ECU but no promises

also, make sure to verify what flash config your ECU's are!
some ECU's are 2mb only, so all internal to the MCU. other's like mine and newer EDC17CP14's (which are REALLY EDC17CP20's with a different software..) are 4mb, 2mb internal on MCU and 2mb external on a dedicated flash
with the PN, i may be able to give you a PDF of your ECU functions from bosch. likely wont be a 100% match to your ECU, but searching for the data you want in your BIN can be done by copying some arbitrary data a known number of bytes ahead of or behind what you want to change.
then search your BIN for that arbitrary data copied from the reference BIN in the bosch documentation, apply your offset to get to the data you wanted to see/edit, boom!
nice! genuine openport 2.0 is the way to go. china clone PCMflash is fine for the software side. PM me for more info and links on what you should buy
about the asm stuff, yeeeeeah it's a bear!
i've been neck deep in the power steering firmware for a while now. i'm largely still clueless to how asm/ghidra/embedded works. like if you threw me into a new binary in ghidra like our ECU's, i would be clueless.
thankfully with the EPS, we had a wonderful starting place because of Willem's blogposts for the EPS patch with our self driving stuff