Thanks for the suggestions and the experiment! It's interesting that it can be done, so that suggests something that may be specific to my set up.
I am working on Windows 10. I found texture files with the download which I assume were meant to be linked via an mtl file (or just manually) and I figured I could link them myself after the import. They are jpg files and seem perfectly OK when opened in other applications (as simple jpg files I mean, I don't know whether there might be something pathalogical about the UV mapping process with them). I've never delved too deeply into UV mapping so the possibility that the absence of normals might cause me an issue isn't something I've considered before. In any case, the complete crash to the desk top is a little unfriendly and I will be extra careful to save my scene before I try any retexturing like this in future!
In this particular case, the model was only going to be a very distant background object to lend scale to the scene. I found that I could apply a simple flat colour texture to each shader and that's actually fine for this usage, where the POV is not close enough to require better textures. I would like to find out a little bit more about what's going wrong here, though, just for future use, so I will try and come back to this, perhaps using Poseray or another import/export process.
I've learned that working with figures and exporting them as obj files for Terragen seems to work better from DAZ studio than Poser, with the latter exporting obj files that don't pick up textures, whilst the former works fine and successfully pulls together all the textures with the obj file. Again I am only doing this for distant tiny figures, so I am not too worried about texture fidelity but it is still nice when it works out of the box. Interestingly, DAZ Studio seems to offer a lot more control over the way the obj file is created than Poser does including an explicit option for the creation of normals which may account for the greater success I had using that export method.
