I think it holds in the scenario you're talking about. If ISP's had different rates at different times and made those times public, you could choose to stop you

I think it holds in the scenario you're talking about. If ISP's had different rates at different times and made those times public, you could choose to stop yourself from using certain things at those times, but it's your choice (or whoever you decide to let make that choice for you, but that doesn't have to be the ISP).