Shape Select node
The Shape Select merges two or more 3D textures by assigning them based on input selection shapes

Inputs
The Shape Select node accepts two or more 3D texture inputs:
The default texture, used for all samples that are outside the selection shape
The selected texture that is assigned to all samples that are inside the selection shape
The shape where the first input is applied
This node is variadic, and more inputs and associated selection shapes can be added.
Outputs
The Shape Select node generates a merged 3D texture.
Parameters
The Shape Select node accepts a smoothness parameter that defines the width of the area where textures are mixed.