Note that in version 1.5 the rules of work with the registry files have changed (with the extension .reg).
Before it was like this
Game engine loaded only /set/registry.reg
Everything else (from the folder / set / registry and not only) had to be explicitly added to /set/registry.reg through directive (include ...)
How it works now in version 1.5.
The engine finds and loads all the files with the extension .reg. And each file is loaded into the registry root. As a result, registry files are split into two disjoint groups: those that relate to the scene, are in /set/registry, and those that are to the interface - in /interface/registry. But this is just a convention.
What it gives?
Now you can create your own mystuff.reg files in your mods and packgages and the game will see them with no problems.