> I fear now that httrack will delete all the old
> content of the posts (because mytumblr/page/2 has
> changed) and re-download all the posts.

The purge happens at the end of the update.
Since the index pages have all changed (2 -> 3, 1 -> 2...) they will all be
download.

> Is there a way to be sure, that the "old" posts dont
> get downloaded again, just because they moved their
> position within the pages (post 91 went from last
> position on page/1 to first position of page/2).

The old posts will still have the same URL and those haven't changed, so they
will not be downloaded.