That absolutely will not work on a Civic because unlike most other cars, the engine rotates counterclockwise viewed from the front. Thus it will only make the bolt tighter.

For the rounded keyway, just put it back together and be sure to get the bolt properly tight so it doesn't come loose again. The keyway is mostly to set up the timing marks on the "balancer" pulley. You can make new marks by probing in cylinder #1 to find TDC, then measure to put the other marks on.

 

I once used jb weld to make another slot for the keyway. This was a temporary fix so I could line up the pulley with timing mark. Make sure the crank pulley and the bolt isn't damaged since the pulley was loose. More than likely the pulley will get loose in the future. Knowing that I used an ample supply of locktite on the pulley and bolt. You should start looking for another motor.