[Xrystal]

Sounds like it is linked to when the Blizzard Addon is loaded and you make your change, similar to your other query. If you haven't already tried it, use the ADDON_LOADED event to ensure the addon is loaded before you make your changes. The way I do it in lua for simple event watching is as follows.

local frame = CreateFrame("Frame")
frame:RegisterEvent("ADDON_LOADED")
frame:SetScript("OnEvent", function(self,event,...)
     local args = {...}
     if event == "ADDON_LOADED" and args[0] == "Blizzard_ArenaUI" then
        -- Make any changes you want here
     end
end