I applaud you for undertaking jobs like this, but surely they are best left for experts with the correct training, knowledge and diagnostic equipment. The worry I have, is that without it, you won't know whether you have undertaken the job correctly until you or the next owner have a crash and find out that the airbags were correctly deployed.
I can see, and have sympathy with, both sides of this argument.
On any car - even one you have just bought new and driven out of the showroom after a full and properly conducted PDI - there is a remote possibility the airbag system may malfunction. There is a very tiny probability that an airbag might not deploy correctly in the case of a serious crash, and an even smaller probability that one might unexpectedly deploy during normal driving and cause a serious crash. (On early RHD 500's, the first situation was actually quite likely as the original software was not fit for purpose; there is a VOSA recall over this issue).
Repairing an airbag system after it has been deployed may increase these risks and it is self evident that if the system is not restored to full working order these risks escalate rapidly. Equally a rebuilt airbag system will work exactly as intended if the job is done correctly using parts which are fully functional.
Professional repairs to airbag systems are frighteningly expensive - most cars are written off if the airbags have deployed in an accident. Getting access to both suitable parts and the necessary technical information is fraught with problems - new airbag components are extremely costly and the relevant information is not easy to find in the public domain. Secondhand parts may make an otherwise uneconomic repair possible, but there is no way of guaranteeing their integrity. If not correctly stored, they may not function properly when needed; in particular, there is no way of knowing if they have not at some point suffered from water incursion; never a good thing for explosives.
Manufacturers and franchised dealers hold most of the cards and, were it not for the work done by the likes of the OP, many otherwise repairable vehicles would be writted off. Building an open knowledge base, accessible to anyone with an internet connection, is our only real defense to being held to ransom whenever an airbag fault (or indeed a fault in any proprietary system) needs fixing.
That said, the risks of working on complex systems when the necessary parts and technical information are not available are not insignificant and even the most competent engineers can't mitigate them completely.
In some jurisdictions, salvaged airbag components cannot be sold or reused and it is unlawful for any person to work on an airbag system if they do not hold appropriate accreditation and certification. If this applied in the UK, it would certainly make life both more difficult and more expensive for anyone facing any kind of airbag issue outside warranty.
Another issue which can't be ignored today is the litigatious nature of our society. In the admittedly most unlikely event of the worst occurring, the current obsession with blame and punishment would likely make life extremely uncomfortable for anyone who had previously worked on a car involved in a fatal collision where the condition of the vehicle may have been a factor.
If someone were to lose their life as a result of an airbag failing to deploy, and it were subsequently found that the system had been previously repaired by an unqualified person using secondhand parts, that person would very likely be facing a mansaughter charge.
