Question: During a battle between two extremely powerful space wizards, a beam of magical lightning has blasted a perfectly circular hole around 10 feet in diameter directly through an Earth-sized planet. In and out like a gunshot through paper. How would this impact life on the planet after this event, if at all?

NOTE: The incident occured about 150 miles south of the planet's north pole.

Answer: 
In the dept of the Earth the hole would be filled in moments. In the surface two things may happen, depending on the state of the dynamic system that is going on beneath the crust:

* some minor seismic activity happens because of a sudden (and quite little) lack of pressure, deep landslides block lava from coming out of the hole, but still a lot of heat would keep coming out of it (geothermal spot).
* lava smashes out in a huge jet. I think it's unlikely that a volcano would set there permanently anyway.

If you want to know precisely (well, not 100% precisely) you have to tell the exact spot to a geologist. There are models of the activity of Earth's mantle that can predict what would happen more precisely.
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> How would this impact life on the planet after this event, if at all?
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Say good bye to life.

An end to end hole on Earth would not be stable, and would collapse under the gravitational force exerted by the planet. That would alone would release a large amount of energy which would surely evaporate the oceans if not even melt the crust.

Add to that also the kinetic energy dissipated by the projectile when crossing through the entire planet, and the picture gets only worst.