Workflow using Terraform pro / World Machine / UE5

What steps does one need to take using Heightmaps in a worldmachine/terraform pro pipeline?

I use Global mapper to do all my shape files, and also extract my source heightmap into Geotiff format.

Then as normal, I bring all of that into Unreal and works as expected.

For the Masks, I use Worldmachine and the source heightmap to generate everything. The Masks go out as PNG for the landscape in Unreal. 

but what if I want to use a modified version of the heightmap that is generated in World Machine?

I hear people mention something about manipulating the header of a Geotiff. 

Can anyone explain to me this process?