Thank you, dr. Mike. Yes your answer is helpful but not what I hoped for.
I would prefer nr. 2 as I feel particularly Google is a bit too effettice and I do not like seeing semiprivate comment discussions showing up on irrelevant search terms in Google searches.
My idea was this strategy: select "block search engines" , and in the future put things of informational value for the blog topic on external, searchable sites, then link to them instead of placing them within the blog account.
However, things of informational value for the blog topic already created and linked to from Google etc, should still be searchable and keep its Google position on certain search terms.
But now I realise that is not an option. Maybe there is another workaround anyway. Otherwise I might find one.