I've made several RTV and silicon molds in the past, but almost always using a resin item as the master. A resin master is always easy to remove from the mold. A few years ago I picked up a hydrocal/plaster inexpensive souvenir item in a foreign country. I cleaned it up, detailed it, and made it look more like a real miniature rather than a souvenir. It is a stone wall section with relief carving (Ankor Wat, Cambodia). Measures about 4" x 6", and about 1/2" thick. I would like to make a mold of this, but, being hyrocal/plaster, is more fragile than resin masters. Is there a safe or easy way to remove the master from the mold material without damaging or destroying the master?

I don't think you'll have a problem with this material. After the RTV cures, can't you just carefully push from behind the mold like popping it out?

Perhaps what you should do first is seal the master with some kind of shellac or other sealant. That should keep the master intact so that it doesn't break apart. Unfortunately , I don't know a brand to recommend but I'm sure someone here will.

Yes...sealing and maybe some kind of lubricant to keep the master from sticking in the mold. There are lots of rough edges and deep cuts on the master.