Some of the material expression reference documentation is slightly incorrect, I have recently been experimenting with a rock shader to find that some of the old limitations no longer apply (which I’m thrilled about btw :))
The ‘Transform’ node used to be mutually exclusive against the Vertex Color node, something to do with limitations? That seems to have been rectified now, as I am using a Z_Masked material that uses a transform node, alongside vertex-painted layers as well. This maybe purely because I’m blending between different material attributes, but if it is, this is at least a way to get around the previously very annoying limitation!