Join Date: Feb 2013
Location: Aussie in Sweden
Diagnostic cable and the software isn't really all that expensive nor is it an on-going cost. Once you buy them you have them forever. So the cost there is quite negligible. Plus I would say the cable is a MUST for any DIY'er. For most things you don't need to buy the software (Airbag I think you do) but even then its relatively cheap considering its cheaper than even the most basic of garage visits.
Regarding swapping the ECU, without knowing for sure, I would suggest that its not as simple as just swapping the airbag ECU as there may be issues with the body computer communicating with it. But wait for others to chime in here as I am in no way certain, its just my inkling.
2000 Alfa 156 Sportwagon 2.0 TS CF3
2002 Alfa GTV 2.0 TS CF3
1983 Porsche 944