That's an interesting thought. But I've never heard of such repairs (rebuilds) myself.
Many years ago we came across "soft" x-ray tubes in military (battle field) radiography sets. They were simple (fixed anode) tubes, but even then the government didn't go for the evacuation (re-pulling the vacuum) option. Not sure if the idea was even costed (probably not); instead new equipment - complete systems (of lesser utility) - was procured.
By the way, there was a time when x-ray tubes were still manufactured in the UK; I remember visiting the factory (fifty years ago now).
Maybe @MikeX might like to respond.
