Yahoo Messenger Tweaker would be the best utility to customize Yahoo Messenger 9 settings and remove advertisements.
Yahoo Messenger Tweaker Features:
- Yahoo Messenger advertisement removal.
- Tweak to enable use of multiple Yahoo ID's in different windows on same computer at same time (Polygamy).
- Tweak to enable Tabbed chat windows.
- Change Yahoo Messenger Title.
- Customize login flash animation to your choice.