It's safe to assume that your talking about an open system because an isolated system or closed system is where you can only increase the entropy and not decrease. If you consider every factor and parameter, the net increase would always be will always be positive.

I don't really think that applying this principle can help us. Isn't this mostly applied with heat and matter? What is the measurable property of Bitcoin mining that you could correlate with this?

P.S. I will be waiting for your "application" of third law of thermodynamics. lol