Replace text with more than just links?

I know you can easily set it to replace text with links, but I’d like to replace text with some custom HTML that will highlight and underline some text and include “title” tags.
The reason some people on our forums use tone indicators, but for new people they need explaining a lot. If I could have an abbr tag wrapped around them with a title tag explaining what it means and a link to the list, that would be perfect.
Is this possible? Would it require a theme component? I have no idea how to make one of those.

Discuss this on our forum.