# How do I add custom logic to a World of Warcraft internal LUA event using an addon?

I'm trying to show a bit of custom text directly after mount names in the World of Warcraft Mount Journal. I've exported the Blizzard API code from the World of Warcraft client, found the method I want to override, copied it to my addon and attempted to register it as a replacement script using MountJournal.ListScrollFrame:SetScript(). However, this doesn't appear to be working.

I've done some investigating, and apparently I need to some magic involving frames and registering events? I'm not sure.

My addon source code can be found at https://github.com/nzall/WarcraftTransportAcquisitionRating/blob/master/warcraftTransportAcquisitionRating.lua. The relevant part that I'm fairly sure is broken can be found below. I'm using Ace to simplify development.

function wTAR:OnEnable()
MountJournal.ListScrollFrame:SetScript("OnUpdate", MountJournal_UpdateMountList);
end


What is the proper way to do what I'm trying to do? Or otherwise, if I'm trying to do the wrong thing, how should I do it instead?