Asset Registry should work after package as it is runtime module, you can tell header file location:
Runtime/AssetRegistry/Public/AssetRegistryModule.h
If it was “development” or “editor” that would mean that module is avable in shipping build
I also don’t know why you need asset registry to populate UClass* array, information about classes are held in reflection system, this will allow you to access both C++ and Blueprint classes, while in asset manager you can only get blueprints as far as i know. You can search for UClass* using UObjectIterator and filter down:
You should do this once on game start up as it is expensive process. You should also avoid doing that in constructor as not all UClass may be loaded during CDO creation.