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On the subject of re-coding the air-bag controller etc, the latest is that it's not possible without some very major alterations involving looms and long-number codes.
However, I have established through my very helpful VW dealers and, independently, Volkswagen Racing, that all the initial airbag de-activated warning is at initial startup is the systems check flagging no connection to the front seats. It then disappears after the systems check is completed. Subsequently, if there is indeed a problem with the car's existing airbags, that system check warning will remain on. So it's all safe!
I'd like to take this opportunity to thank Gary for his willingness and efforts to help.