is it possible to use different uv attribute name in mtlx? (for mixing shaders)

There are a few nodes for bringing in specific attributes/primvars such as MtlX Texture Coordinates or MtlX Geometry Color, but you can always just use MtlX Geometry Property Value instead. Use it to bring in uv2 or whatever it's called and set the signature to Vector 2 if you would like.