[Slakah]

Are you sure you need an event to do it, I'm pretty sure you could just do.

        MainMenuBarLeftEndCap:Hide() 
        MainMenuBarRightEndCap:Hide()

as all Blizzard code is executed before addons (unless it's LOD).

and heres an example of a super simple event handler:

local function OnEvent(f, event, args)
   if event == <Event 1> then
      --Do stuff
   elseif event == <Event 2> then
      --Do other stuff
   end
end

local f = CreateFrame("Frame")
f:RegisterEvent(<Event 1>)
f:RegisterEvent(<Event 2>)
f:SetScript("OnEvent", OnEvent)