... How did I never think of hiding images within R/B/G channels themselves? Oh my god, what a terrific trick!
Basically, while doing a great tutorial for UE4 materials from www.gametextures.com (link below), they also happened to teach me a trick that I feel like I should have figured out ages ago - having specific images in your R, G, B and alpha channels for use in your blueprints.
"But what does it all mean, Chris?"
Well, basically it's an easy way to hide anything you don't need specific color information for within an individual texture node, and individual file. I'm not going to get into the meaning of all of that, but basically you can create much more efficient file and material structures this way.
So it's a much more efficient way to have clouds/grunge/scratch textures in a single source, in this case, for a landscape. It makes it really easy for me to copy/paste this commented area and apply/modify it for whatever source I like.
Well, this is my displacement-map landscape material that I made, with some textures I also made from scratch, just kind of randomly sprayed around. The variation in shading of all grass types makes for a lot of unique areas... and that's from me literally just spraying it around at 50% tool strength, not actually painting it nicely.
I wish file moving/restructuring and asset management was more efficient, but otherwise UE4 and I are proving to be very good friends... I daresay a love is forming between us.
Here's basically how you do it. I learned in a comments section I linked below, as well.
Gametextures.com tutorial: https://www.gametextures.com/using-gametextures-in-unreal-engine-4/
Separating layers into channels: https://graphicdesign.stackexchange.com/questions/79318/how-to-put-a-layer-into-one-of-the-rgb-channels