Answer:
Create a special landscape material, set the base material as a texture that you can swap out (parameter) in your instances. as you paint the landscape you “Fill” layer 0. (you have to get the right scale for the UVs using landscape layer coords. shouldn’t be too hard since the size will be precise)
Then you can overlay the other layers as you normally would.
and eventually remove the 0 layer from the material.
The real way:
I would suggest you learn how to use Qgis - it’s free.
It lets you manage your DTM and pull satellite imagery.
It’s complicated. it will take time.
Qgis will allow you to keep the data of the tile and satellite in relation.
It works with Geo Referencing, Extents, and Columns instead of pixels.
Given this. the program will let you color and export your digital terrain model in different ways based on height data. as well as give you a 1:1 relation between what you export and the satellite image.
Meaning, you can export the satellite image, and create a manual “splat” map to use during tile import.