"...However, I'll caveat this with certain car related things such as replacement key fobs or ECU's are probably justified in having to be 'registered' to the relevant car in question..."
Fair point but the flip side of this is my use case. I just bought my 17yo son his first car - a 53 plate Corsa.
The remote key fob was nadgered, so I bought a brand new replacement off the bay for about 6 quid including postage (and the battery!)
For another 15 quid or so, I bought an Opcom unit as you cannot use the "ignition on to second place and hold a button down" method with a new key.
It was a bit trickier than I was antiicipating, requiring an EEPROM dump and binary viewer to get the security code, but once done, it was trivial to program the new key.
I did that, and set the doors to all open on a single press, rather than drivers door first, then a second press for the passenger door.
But...the options were seemingly endless. I didn't poke and play because I didn't understand what the knock on effect or direct impact may be of my actions, but - and this is the important bit - I had the option. And, had I screwed it up, I'd have had no one to blame but myself and had that then meant costly repairs at a dealer, so be it, but....I could have
My car (well, my son's but you get the idea), mine to bork however I see fit.