Question A simple (as possible) Terrain texture changer

Hi
I have a terrain that represents the surface of a coal mine. The main focus area is approx 300m x 300m.

An explosion (and smoke) simulation runs that emulates the destructive nature (see 3rd image, screenshot from blast sequence).
I need that surface area to then darken (gardually lerped if possible) as if covered in fine dust settling.

I'll settle for a simple swap if necessary but it would be nice to see the transition.

I'm finding it hard to get any clear solutions searching the net. Some are overkill or deeply complicated.

Does anyone know a simple way to swap the splatmap that holds the texture data? I understand terrain data is not so straight forward,

Many thanks for looking!
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