Is PluginLibrary the best option? The same author also has a plugin called Hooks for 1.6 -- is that compatible with 1.8? Is this a horrible, ill-advised idea?
Specifically, I need a hook for when MyBB parses a quote.
PluginLibrary if you want to make the edits programmatically (in your own plugin), Patches/Hooks plugin if you want to do it in your Admin CP. Sorry I didn't post those yet to the mods site but you can download from GitHub, it should work fine with MyBB 1.8.
Or convince the MyBB team to add it as official hook in a future MyBB version.
Thanks everyone! (: I ended up using PluginLibrary and requiring it as a dependency for my plugin.