Basically, for our forums, I needed to customize buttons (to add icons).
You can browse it here :
http://www.pathfinder-fr.org/Forum/ .
Until now, I edited manually all concerned aspx/ascx for each YAFNET release.
But today I decided to submit
a pull request to integrate this feature in the official code, as it's a safe modification for all users, and can help anyone interested in theming.
Please note that I encoutered issues to only highlight modified lines, as the migration from hg to git seems to have broken line-endings. I think that the commit always trigger a full page change, then following commits will better handle differences.