I’m not sure I understand the question. CUV0 and CUV1 are named inputs, and they are already correct, no need to sort them.
If you only add 1 customUV input, that will be CUV0. If you add another, that one will be CUV1 and so on. CUV0 would be referenced in the pixelshader by using a texturecoordinate node that has index to 0. Get it? Index 0 grabs CUV0. Index 1 would grab CUV1 if there is one.
It doesn’t matter which one you use as long as you are consistent. I would normally put a panner in CUV1 so that CUV0 is blank, so there can still be non-panning alpha masks used. If everything in your material uses the same panner then by all means simply use CUV0 and then you will essentially be erasing your base UVs.