Is your feature request related to a problem? Please describe.
Cannot add new entities to existing mob soul type

Describe the solution you'd like
The ability to add/remove entities from existing mob soul types

Describe alternatives you've considered
I've attempted to create my own mob type with the entities I desire (spiders, cave spiders, a custom spider), but because they are a part of an existing mob soul type, the mob soul type doesn't even show up in game. This occurs even when the spiders type is set to enabled: false.