The easiest way is just live with it: Split off the first 9 while keeping the full story as posted until book 10 is done, then split it off as it's own book. There's duplication, but you mostly get what you want. But I acknowledge that 1M+ word stories can be hard on ereaders.
Alternatively, there is a somewhat undocumented feature you could use:
first_chapter (and
last_chapter), when set in personal.ini, have the same affect as a chapter range after the URL during download.
Download as is, use EpubSplit to extract the first 9 books to new books, then set in personal.ini:
Code:
[https://www.fanfiction.net/s/10465135/1/Legend-of-Spyro-Path-of-Delusions]
first_chapter:205
You'd probably need to "Update Always" on it the first time to discard chapters 1-204.
I've used
first_chapter before for doing exactly this; splitting lengthy stories into parts.
You also need to clear the Identifier:url settings in Calibre--I assume you will already be changing the titles--to avoid updates finding the split off stories.