Hi James,
I imagine the script could work something like in attached gif. It doesn't have to be very smart, simply checking if selected object has assigned Corona physical, or legacy material and then insert randomizer, or triplanar between material and already existing maps. In case of randomizer, the script should perform additional check and see if there's triplanar existing in the shader tree, in that case, it should insert randomizer after the triplanar. I think that would cover majority of use cases.