A new pin should come in a service kit. Or it will work just fine with no pin as long as nobody plays with it. Just check the cover occasionally. Converting to an adjustable viva would require a new case with the adjustable viva components. Probably better to just get a new 2nd stage if you really need that capability. Why do you think you need that anyway? While it might be nice on an alternate, I prefer a higher performance reg with a user adjustable,cracking pressure in that role. On a stage or slung pony which is left off when not in use, the simpler the better so no adjustment necessary. In fact, due to extra complexity, some might consider it undesirable.