Will a board blocking my air conditioning break it?
It's pretty hard to say without knowing more.  The general idea is that the fan that's blowing hot air at you is supposed to be drawing cool air through a series of fins.  The fins are full of hot liquid, and the cool air blowing through the fins draws heat from that hot liquid.  Then it exhausts that now heated air.  

So it should be drawing in ambient ("normal") air and exhausting heated air.  As a broad generalization, exhaust air is noticeably warm, but not so hot that you can't stand it on your skin.  One situation that can occur is the intake and exhaust air can be so close together, or be in such an enclosed/confined area that the heated exhaust air gets pulled in as intake air, gets heated again, and exhausted as even hotter air.  And then pulled in and heated again, etc.  This condition makes the unit very inefficient, and if it's bad enough, it can even be dangerous.

It's a matter of degree, so if the discharge air at your unit is so hot that you can't stand it, then there's probably a fair measure of this unwanted exhaust/intake air recirculation going on with your unit.

I said all that to say this:  You're fine to deflect the hot discharge air in any way that you wish, as long as you don't cause (or worsen) a case of exhaust/intake air recirculation.