Maybe not banned as a matter of course BUT as part of good engineering practice certainly tested to AT LEAST the rated safe working pressure, ideally 1.5x this. When I say tested I know the arguments of cost of independant testing but in my view a test carried out by and a certificate issued by the modifier that outlines method of test, pressure acheaved during test, name and signature of tester and date of test, to be given to and/or kept by the owner of the modified cylinder. Hopefully this will dissuade rogue practitioners passing off dodgy work and add value to the work carried out by good engineers out there. Most importantly this will increase safety, not just to that cylinder user but also to other round them.
I know its been said that there has been very few of these incidents, maybe there have only been a few, but we should pay more heed to consiquences, ask ourselves what is the worse than can happen, as has been tragicly illustrated bt the recent unfortunate incident that has caused us to discuss this. Just because It has not happened to us or those round us SO FAR does not mean it will not happen tomorrow. We should be mindfull of this and with this in mind try to carry out REASONABLE steps to keep ourselves and others round us safe, and to keep our sport a safe sport.