Can you remind me what was involved in the crystal mod? I seem to recall the rehaut ring on the new crystal needed modification. Can you remember what size crystal was used, I`m guessing it's a standard Sternkreuz ATC?
I`m sure I`ll get asked at some point whether I can do this job for someone, usually I won't get involved with modifications but if it's straightforward I don`t mind. Did you test the watch for water resistance after fitting the new crystal? Provided it fits tightly it should be OK up to 3 bar at least, probably more.
I've worked on a couple of the PRS 25 40mm versions with the original acrylic crystal (which is no longer available), replacing the original with a Sternkreuz ATC out of necessity because the original has cracked or loosened.
PM me with details if that helps.