uhh I’m not sure I get exactly what you’re trying to do, but…
Sounds like you want something like this ?
First of all for such a thing you don’t really need to use plugins, unless your project is already structured as such. The whole point of plugin paks is to have distinct asset paths and asset registries that will all be added together when the game loads all paks, to avoid asset conflicts and make them discoverable via asset registry searches. The point of patch paks on the other hand, is to leverage asset conflicts to completely override game assets with new assets in the patch pak.
Then the simplest method would be to NOT include the child blueprint in the pak project.
Alternatively, if BP_BaseClass is the only asset you want to override, consider making a patch pak with ONLY that asset (no need for dependencies, no need for child, no need for asset registry) kinda just like the picture above.