MikeJones the ideal solution would be to register a custom bbcode or other markup, then write some logic that checks permissions when the post is saved.
I can't think of any extension where we restrict what can be inserted based on who edited the post, as usually everyone is allowed to use all of the markup added by extensions, but it should be doable.
If it's not important to check who edited the post but just who owns the post, it should be fairly easy to design a bbcode that only renders into an ad into posts made by users that belong to specific groups, and otherwise just show the bbcode as-it or as blank.
