[Nibelheim]

Hmm, you're right, that won't work at all. You'll just need to hook it once like you were doing:

hooksecurefunc('ActionButton_Update', function(self)
        for _, icon in pairs({
            self:GetName(),
            'MultiCastRecallSpellButton',
            'MultiCastSummonSpellButton',
        }) do
        local macroname = _G[self:GetName()..'Name']
        if (db.HideMacronames) then
            macroname:SetAlpha(0)
        end
    end
end)

And reload the UI to apply the changes. Hooking it again in UpdateStuff won't do anything.