Changing original poster
 

Is it possible to change poster of the post?
Exem:
User A make some post and I change that user B made that post.

I don't know if there's an easier way, but this is what i do

Post as User B in the same thread.
Merge the original post and the new post together.
It'll have an option to choose who it displays as.

There is a modification to change the poster of the post if this is something you plan to do regularly.

Do you know which modification?

I don't know the name of it, no. But, I'm sure you can search it out.