Seems like it might be prudent to first try extracting 35% of the heat from a volcano smaller than the Yellowstone Caldera. We might learn some things, and if we get it wrong the consequences don't result in widespread starvation.

That said, it's obvious that this plan is just the start of serious investigation into how we can engineer mitigations to an eruption at Yellowstone. I would be interested in seeing a model of the impact that surface-level cooling would have on the pressures deeper in the system. If we prevent an eruption now, are we making it worse in the future?

Other solutions I can envision might be to deliberately trigger smaller eruptions over longer timescales at the boundaries of the caldera. We could also look at large-scale mitigations for volcanic particulates in the atmosphere, including solutions that may require several hundred or thousand years of advanced preparation for success. If we could control the impact of a significant yellowstone eruption to a single hemisphere, or limit the duration to a single summer, most ecosystems would be able to recover quickly.