MyBB Community Forums

I would like a plugin that allows a simple way when editing a topic to change the post author and update the post count.

Willing to make a payment via Paypal if this is done quickly and without any bugs.

You can subscribe starting from 3$ to download the plugin @ http://www.shadeplugins.tk/index.php

Just in case it is useful:
http://mybbhacks.zingaburga.com/showthread.php?tid=643

This might be overkill for what you're looking for, but the Advanced Account Switcher allows users to switch post authors after posts have been made (if they made it on the incorrect account, for example):

http://doylecc.altervista.org/en/switcher.html