Custom trigger
function(event)
    local slotId = GetInventorySlotInfo("BackSlot");
    local link = GetInventoryItemLink("player", slotId);

    if link == nil then
        return false;
    end

    local itemId, enchantId = link:match("item:(%d+):(%d+):*");

    if enchantId == "5436" then
        return true;
    end
end

Custom Untrigger

function(event)
    local slotId = GetInventorySlotInfo("BackSlot");
    local link = GetInventoryItemLink("player", slotId);

    if link == nil then
        return true;
    end

    local itemId, enchantId = link:match("item:(%d+):(%d+):*");

    if enchantId ~= "5436" then
        return true;
    end
end