[russnes]

My concern is fundamentally whether or not we are siphoning energy out of the core faster than it would otherwise escape.

Since the layers are directly connected, it doesn't sound like to me that you'd have to dig into the very core for that to happen.

Of course at the current state of affairs the effects are miniscule, but it doesn't sound like a very good investment as something to potentially scale up in the future to where it will actually matter.

If it turns out to be a problem, how hard would it be to insert fuel back into the earth's core to sustain the magnetic field?

[ncmncm]

Literally impossible to do. And, also, absolutely pointless to worry about.

In another century, if we don't blast ourselves back to the stone age first (increasingly likely), energy from hydrogen-boron fusion will dominate wherever solar is impractical, and the geothermal wells will become too expensive to continue operating. So, either way, the whole process is an imperceptible blip.

[russnes]

OK, good. But yeah the high likelihood of returning to the stone age repeatedly makes it even more important for the magnetic field to sustain for as long as possible.

[ncmncm]

We will never have any way to interfere with the planetary magnetic field, in any circumstance.

Blasting our way back to the stone age will succeed in chopping off CO2 output suddenly, though. The climate could then return to normal in only a century or three, if the sudden change did not instead trigger an ice age or something.

[lazide]

It is very, very, very unlikely to make any noticeable difference even on geological scales.