How can I alter "FeatureType" of a Google Map

Currently, I don’t see a way through the UI to do this to a Google Map.
I’d like to know how to add additional “custom” code to execute on a Map.

per this thread:

Simple JSON to further customize the appearance of a map.

This is the map I get with GoogleMaps now (cluttered):

This is the map I’d like (less cluttered):

You can see how FeatureTypes are being shown/hid here:

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