[Phanx]

Well, here is one problem:

Originally Posted by lerb local function Grid_AddBorder(f) CreateBorderLight(frame, LeUI.media.bordersize, LeUI.bordercolor, LeUI.bordercolor, LeUI.bordercolor, 2)

Here is a more commented version of what should, theoretically, be working code:

local function SkinGrid()
    print("SkinGrid")
 
    -- IMPORTANT: If Grid2 gives each of its parts a cluttery global name,
    -- leave this line commented. Otherwise, uncomment it and adjust as
    -- needed:
 
    -- local GridFrame = Grid and Grid:GetModule("GridFrame")
 
    if GridFrame and GridFrame.registeredFrames then
        -- Grid is already loaded. Go ahead and skin the frames.
        print("Grid is loaded!")
 
        -- This function will be used to override the default border
        -- coloring method on a Grid frame.
        local function Grid_SetBackdropBorderColor(frame, r, g, b, a)
            if a and a == 0 then
                -- Instead of hiding the border when it's not showing a
                -- status, we want to reset it to the default color.
                frame:SetBorderColor()
            else
                -- Otherwise, we want to ignore the status's alpha value
                -- and always show the border at 100% opacity.
                frame:SetBorderColor(r, g, b)
            end
        end
 
        -- This function adds a border to a single frame.
        local function Grid_AddBorder(frame)
            -- Check if we already added a border to this frame:
            if not frame.SetBorderColor then
                -- Tell Grid the border is very small, so it will adjust
                -- the insets on the frame accordingly:
 
                -- IMPORTANT: You will need to find the equivalent
                -- function in Grid2 and change/uncomment this line:
 
                -- frame:SetBorderSize(0.1)
 
                -- Actually add the border:
                CreateBorderChat(frame,
                    LeUI.media.bordersize,
                    LeUI.bordercolor,
                    LeUI.bordercolor,
                    LeUI.bordercolor,
                    2)
 
                -- Hook the frame's border coloring method:
 
                -- IMPORTANT: Find out if this is necessary with Grid2
                -- and/or !Beautycase, and uncomment this line if so:
 
                -- frame.SetBackdropBorderColor = Grid_SetBackdropBorderColor
 
 
 
                -- Disable Grid's method for changing the border size:
 
                -- IMPORTANT: Find the equiavlent function in Grid2 and
                -- change/uncomment this line:
 
                -- frame.SetBorderSize = noop
            end
        end
 
        -- Loop through all of the frames that have already been created
        -- and add a border to each one:
        for frameName in pairs(GridFrame.registeredFrames) do
            Grid_AddBorder(_G[frameName])
            print("Added border to", frameName, "in SkinGrid.")
        end
 
        -- Hook Grid's RegisterFrame method to catch new frames when
        -- they are created in the future:
        hooksecurefunc(GridFrame, "RegisterFrame", function(frame)
            Grid_AddBorder(frame)
            print("Added border to", frame:GetName(), "in RegisterFrame hook.")
        end
 
        -- Return true, since the function successfully ran.
        return true
    end
end
 
if not SkinGrid() then
    print("Grid not loaded.")
    -- A nil return value indicates that Grid was not loaded yet,
    -- so we need to watch for that:
    local f = CreateFrame("Frame")
    f:RegisterEvent("ADDON_LOADED")
    f:RegisterEvent("PLAYER_LOGIN")
    f:SetScript("OnEvent", function()
        if SkinGrid() then
            -- Grid is now loaded, and has been skinned.
            -- Stop listening for addon loading events.
            print("Grid is now loaded. Stop listening.")
            f:UnregisterAllEvents()
            f:SetScript("OnEvent", nil)
            SkinGrid = nil
        else
            -- If SkinGrid() returned nil again, that means Grid is
            -- still not loaded, so we should keep listening.
            print("Grid is still not loaded. Keep listening.")
        end
    end)
end

Comments beginning with "IMPORTANT:" indicate sections that may need to be changed depending on how !Beautycase and/or Grid2 work internally. The code should work as-is, but if something doesn't work, those are the sections you should check first.

Not tested in-game, so may contain syntax errors.