I have a Passat 1.6 blue motion 2014 and the car has suddenly becomes immobile when trying to start and responds with many warning lights,on occasions it does start and run but not for long.I have taken it to a garage and they identified a faulty water damaged ECU and am looking at options currently.Re-cloning could cost all 8-900 GBP with mechanics time.I have investigated second hand and it would be substantially cheaper but with some risks.One supplier has confirmed that he can supply a secondhand ECU with the identical part number of my faulty ECU so on that basis does it still need to be wiped and reprogrammed?
Unfortunately there's still going to be some re-coding needed. You can't just straight swap the ECU in from another car.
Sadly water ingress into the ECU was/is depressingly common on this model of Passat and leads to just the sorts of symptoms you describe.
Since you mention GBP I'm guessing you're UK based - I've heard good things about the services from ecutesting (no affiliation) who can offer rebuilds. Obviously it means you'd be without the car for a few days but it would avoid the need to re-code and could save you a bunch of cash.