First script will rename all open backpacks.
Second will rename the container on open.

UI.Button("Update Button Name", function()
    for i, container in pairs(getContainers()) do
        if not container.window then return end
        container.window:setText("BP: "..container:getId())
    end
end)

onContainerOpen(function(container, previousContainer)
    if not container.window then return end
    container.window:setText("BP: " .. container:getId())
end)