If it was just for Apophis I'd recommend doing nothing. A tiny chance of a hit getting smaller each month with new measurements The effect would be devastating to a thousand square km region (or, with a sea impact, to coastal areas many thousand miles away) but with no long term global effects (not even cooling the global warming).

But in general it is worth trying methods to deflect asteroids, and why not start learning how to do it with Apophis. I'm looking forward to its 2029 flyby when it will be visible to the naked eye. It will come closer than some satellite orbits and will have less than 1/10 of the distance of the moon.

Wolfgang