I see your point, you want to become legendary even with 1 post, it has been discussed few pages back.
You don't have to ask theymos because you can reduce your posts yourself but it will take some time.
I suspect that even if you delete all your post history, your rank won't go down. Since this seems to be what the poster you replied to actually wants, i.e. not remain Legendary with a few posts but turn into a Newbie member again (for his own reasons)...
Did anyone try to delete all their posts?
togesix https://bitcointalksearch.org/user/togesix-310823 who has 1 post and is still Hero Member.