I’d say an engine controller which needs a specific vehicle information to work is going to be difficult. But an ecu that controls say your headlights, depending on the oem it is just a part with unique part# that can be swapped. I work for one of the American OEMs and have replaced a ton of controllers on vehicles (engineering vehicles and customer vehicle). never had an issue. That being said I know German vehicles are next level pita since I do own an Audi. I just wasn’t aware about the coding part for the Audis.