Changing "Color_Texture" to "Image_Map" made it work for me, thanks. I realise that isn't the right way to do it, but it works for my use case which was all I was interested in at present. I have a prop with 275 materials and setting them up would be difficult without scripts.

In a more general case, I think I'm looking at it the wrong way. Instead of looking for a node with a particular name, I should be looking for one which has a particular connection (in this case it would be "the one that's plugged into Diffuse_Color").

Although I can get away with hacking together barely-working scripts for development purposes, it occurs to me that this prop (and another I have in mind) would benefit from being distributed with one or two scripts to help deal with all those materials. Expect more material room questions in the future. ;)