Change Physical Properties of Select Objects?

I want to change the properties of a few objects in the scene without making any changes to the others. CustomPhysicalProperties only will let me change Elasticity, Density and Friction. Is there a way I can change the others like gravity?

Mainly I want an object that bounces off horizontal walls to have half as much gravity

Besides using a BodyForce in the Y-axis. I can't do this because is annoying doing guesswork to figure out how much an object will add to the total weight