The editable children button lets me access the MeshInstance, but only if I make RedVoxel have its own root node and then instantiate voxel.tscn under it.
An inherited scene almost works, except the error that also showed up when I tried to change the Mesh from the editable children mode.
“This resource belongs to a scene that was instantiated or inherited. Changes to it must be made in the original scene.”
godot, the whole point is to make a change to it.
I also tried a solution I saw in this thread, but MeshInstance3D doesn’t have a material property (the editor option to change the material shows up, but doesn’t actually change anything in the rendering).