Is there a way to control where the displacement bump map does and does not affect. Would using the weight paint brush be good? The displacement bump map is made procedurally generated with texture coordinates, noise texture and a displacement map. I followed this tutorial made by Blender Guru. https://www.youtube.com/watch?v=Rh5gAQLtOls&t=456s
You can plug a map into the Scale input of the Displacement node. You may want to do some math on the values as they go in.
I don't think weight paint is available through cycles nodes, but you should be able to use Dynamic Paint a la this answer.
You can use a texture (hand painted or procedural), to control the fac input of a mix RGB node, in which the first input is the displacement texture, the second has a solid gray color (which is the neutral midlevel for displacement and bump).
In this way where the new texture is black you'll have full displacement, where it's white there will be no displacement, with greyscale for transitions.
You can also live paint the texture in rendered view, to check its influence.