How to generate exact terrain form script

My game has currently 4 maps, 3 of which use terrain. Currently there are no issues at all, but I am planning to add much more maps (also using terrain), which will inevitably cause lag on lower end devices. All the things that are not terrain (parts, meshparts, baseparts) are being loaded in and out by custom system when they needed.
I want to do the same with terrain.

Lets say I have this:

How Can I have this removed, but generate exactly like this (all the painted sections as well) from a script when I wanted to? I’ve looked at region3, but am not quite sure how to use it in this case, and if it’s even possible to use it to recreate the painted sections?

I am not asking for a full script, I know scripting and am able to script myself, I’m just asking for ideas. Tho if you could show some example code snippets it would be much appreciated ^^