[Aftermathhqt]

local AfterButtons = CreateFrame("Frame", nil, UIParent)
AfterButtons:RegisterEvent("ADDON_LOADED")
AfterButtons:SetScript("OnEvent", function(self, event, AddOn)
      if AddOn == "Blizzard_GuildBankUI" then
           --pewpew
      elseif AddOn == "Blizzard_GuildBankUI" then
           --pewpew
      end
end)

works very well aswell