You can use readPixels to get data back and create a new texture from that. It could be a bit slow as there’s a roundtrip with the CPU.
You can also create a custom procedural texture that would simply copy the source texture. That would be faster than readPixels as everything would stay on the GPU side.
But I think the easiest way to do it is to use the EffectWrapper / EffectRenderer classes:
https://playground.babylonjs.com/#LG2YYN#2
After 1s, it will copy the diffuse texture of the sphere material and set the copy as the diffuse texture of the ground material.