"addpass" shader (2nd splat textures) blend in at distance?

Hi, I believe unity's AddPass.shader is for the 2nd splat and for the texture slots 4-8.

I am currently using the FirstPass (1-4 texture slots) to stretch 4 satellite images over my terrain (2x2 grid).

But as you can imagine, the close detail is very poor, so my idea is to use the 2nd or addpass splat and textures as "close up" textures, and so to have them blend in when at a distance to the terrain?

Is this something that is doable and would anyone know how to modify the shader to do so?

Thanks