I know where I'm at now then: which is that the Exporter is doing exactly as intended and Blender has a couple of quirks to work around, which is as things always were! But it's definitely workable: inverting a temporary dds and putting it in a more convenient directory isn't a major chore and using a text editor to substitute to and from a temporary string isn't a deal-breaker.
So I find that at alpha stage, I can extract meshes, edit them, add and remove bits, re-weigh them, re-import them and have them appear correctly in game. I am seriously rather impressed and if I were currently wearing my hat I would take it off to you. But sadly, the cat has been sleeping on it. Consider me hatless anyway.
