Hi Gideon,
I will attempt to answer your questions in order, but first an FYI. What you are calling the air shock is not actually a shock at all. It is simply a helper air spring. It does not do any actual damping. It is in fact the original Honda air spring from a 1500 Goldwing that we used to purchase new from Honda to supply with the Valkyrie kits.
1. Yes you can repair the air line while the body is still on the trike.
2. No you will not damage the air spring if you continue to ride the trike.
3. I would definitely not suggest changing to a different suspension system. We do not offer any other suspension for a Valkyrie, and I don't think there is any need to do that if the rest of the components are still in good shape.
4. Unfortunately we don't convert Valkyries any more. We have not offered a Valkyrie kit for at least 10 years as there just isn't any more demand.
5. All of the Valkyrie kits that we manufactured over the years used the air spring.
You can repair your air line simply by removing the fittings from the shrader valve and the spring and cutting about a half an inch from each end of the air line. This will remove the old crimped part of the line. Then just reassemble. That should fix your leak for another 20 years. If by chance it doesn't fix it we have replacement air line and fittings in house.
I hope this helps.