In the case it doees not already exist, please add possilility to use wildcards in the blacklist (in each part of it).

Adventages:

This feature would allow to block multiple items at once, instead of need to list each one in a separate line

This is already a feature, wildcards are supported in blacklists.

Actually I'm wrong - it's not supported. I'm using the RE621 userscript which adds that as a feature.

Since the blacklist is handled on the client-side I'm not sure why this isn't a feature.

The blacklist doesn't support wildcards like the search does.
It would be nice to block all tags that are nearly the same, like for one character owner

*_([character owner name here])

It seems like this feature was suggested and approved 6 years ago. See: https://e621.net/forum_topics/15461