[Xrystal]

I haven't tested these but, looking at the Blizzard Dragonflight code ( 10.2.5 ) these lines should work for the main action bar and pet action bar for retail wow.

for i=1, NUM_PET_ACTION_SLOTS, 1 do
        local button = PetActionBar.actionButtons[i]);
                hooksecurefunc(button, "SetHotKeys",function()
                    local hotkey = self.HotKey;
                     -- do your hotkey additions here
                end)
    end

for i, actionButton in pairs(ActionBar.actionButtons) do
       hooksecurefunc(actionButton,"UpdateHotKeys",function()
          local hotkey = self.HotKey;
          -- do your hotkey additions here
       end
    end

If you are working on Classic versions of wow (1.14.4 and 3.4.3) then it looks like the following could be done instead. Again, untested.

for i=1, NUM_ACTIONBAR_SLOTS, 1 do
        local button = _G["ActionButton" .. i]);
                hooksecurefunc("ActionButton_UpdateHotkeys",function(self)
                    local hotkey = self.HotKey;
                     -- do your hotkey additions here
                end)
    end

for i=1, NUM_PET_ACTION_SLOTS, 1 do
        local button = _G["PetActionButton" .. i]);
                hooksecurefunc("PetActionButton_SetHotKeys",function(self)
                    local hotkey = _G[self:GetName().."HotKey"];
                     -- do your hotkey additions here
                end)
    end

Give those a go and let us know if they work as expected for you.