phpBB.com

Hello! How to add to one user permissions, that he will be able to double posting in specified forum (not in whole board)

What is "double posting"?

http://www.phpbb.com/community/viewtopi ... &t=1054155 This mod features that exact permission and it is forum-based.

Brf wrote:What is "double posting"?

double post is when i post one message, and after this i post second message, and after that i post third message. And those messages are not merged, but three separated messages.

Yes. That is the way that phpBB works.
You would need a mod if you wanted messages merged.