Help making import rules using factories & plugins

I’m trying to get my head around factories, specifically sound factories at the moment.
I’m exploring making my own custom importing rules, for example checking names before importing.

I can happily do this modifying the engine SoundFactory.cpp directly but wondering how I would go about this if I wanted to make this a plugin? For example if the plugin is active then you override the create binary method?

But not sure if this is the correct approach or how to go about that, I tried creating a plugin using the create plugin function from UE4 editor, inheriting from SoundFactory and overriding the Create Binary method but that didn’t work.
Not sure if i’d also have to change the default import priority within the plugin but I can’t see how to do that?

Any information or guidance people have with factories is gratefully received!