There are many mods for custom BBCodes (http://mods.simplemachines.org/index.php?action=search;type=6), but if none of those fit what you want, it is not hard to make your own new codes and tags. SMF 1.0 uses a syntax based on regex's, and SMF 1.1 uses a much simpler array system.

At the moment you can install the http://custom.simplemachines.org/mods/index.php?mod=621 for HMTL based system to add customized BBC tags to your forum. Work with SMF 1.1.x.