As it turned out this is simply too dangerous - these should be left to be loaded from the map data or set manually.
All remaining setups using this feature have either been moved to Initialize or other meta properties that are not affected by map loading.
.def is not the right place for this - it needs to run very early in the process, before scripted actors are loaded, so doing this stuff there means that half the initialization has to be postponed and error reporting is sub-par.
These are now part of RMAPINFO which gets parsed as one of the very last things - it is also where GZDoom is doing some of these things.
The better error reporting also allowed fixing some errors in these definitions.