[Phanx]

Probably:

local function onEnter(frame)
    SetCursor("ITEM_CURSOR")
end

local function hook(frame)
    frame:HookScript("OnEnter", onEnter)
end

local GridFrame = Grid:GetModule("GridFrame")
-- Catch any frames that have already been created:
GridFrame:WithAllFrames(hook)
-- and any that get created in the future:
hooksecurefunc(GridFrame, "InitializeFrame", hook)