After the most painful journey through figuring this out, I finally solved it. And for anyone else that has this problem, here’s what you do. Landscape > Sculpt > Select. Select the area you want to replace. Check “Use Region As Mask”, uncheck “Negative Mask”. Go to the copy tool (Landscape > Sculpt > Copy). Do this, Clear Gizmo Data > Fit Gizmo to Selected Regions > Copy Data to Gizmo. Now, under “Tool Settings” hit “Advanced”, and under “Gizmo Import / Export” leave the fields blank and hit export. This will export your heightmap and weightmap files for each texture you have in your M_Landscape material. Now under “Gizmo Import / Export”, select the Heightmap file that was generated in the “Heightmap” field by clicking the “…”. The heightmap size varies apparently, but for me it’s usually one of the 2 median numbers (the ones closest to the middle). Now click “Import”, if nothing changes that’s good, you’ve verified you have the correct dimensions, if your selection does look different, try some other dimensions or start over from step 1 (I used ChatGPT to help me know which dimensions to use). Then just under the Heightmap section find “Target Layers” and add an array element. “Target Layer File Name” should be the file you want to replace, for me that’s grass, and “Target Layer Name” is whatever the texture you’re replacing it with is named under Landscape > Paint > Target Layers > Layers, so for me I Chose Sand with the layer name “Rippled Sand”. You can now paint the texture, but you’re not done yet because painting will cause the textures it’s blending into to become black. Luckily this part is easy. For every Texture that is blending with the texture you replaced, you’ll want to make another element for (Landscape > Sculpt > Copy > Tool Settings > Advanced > Gizmo Import / Export > Target Layers > Add Element). And then simply Choose the file for “Target Layer File Name”, in my case “Rock.raw”, and the corresponding texture name, in my case “Rock”. Now you can either paint over the landscape using the copy tool, or you can CTRL + V to paste everything being changed in the selected area. I hope this helped, good luck out there.
