Sorry, just to clarify: I've been asked to re-submit the thesis, as the examiners have said the two extra chapters amounts to a substantial change.
It's a very odd result: they've said that it's good, nothing should change re the argument, and that I've done all I can within the given word-count. They feel, however, that by adding an extra 5-10,000 words, it will have a greater coherence.
I've never heard of this, whereby all is well with what has been done, and yet you're asked to re-submit.
The viva itself was great fun; I genuinely enjoyed the experience. The questions were fair but tough, and they all led into a three-way conversation. It's because the viva went so well that I was so shocked to be asked to re-submit.
I just need to get on with the work, but I would love to know if anyone else has been through this.