Cutting out the frown to increase ventilation and is a nice detail to add to your helmet.
Using a small drill bit to create evenly spaced holes, then use a hobby knife and cut out the rest. Sand down the edges to sharpen the corners and even out the size of each hole. Cutting down some emory boards or using a metal nail file works well for this.

Using the provided vinyl decals, place them on the frown as if the vent holes weren't cut out. Then carefully slit down the center of each black section of the decal, leaving enough to wrap around the edges and into the helmet.

Close up view of inside of helmet and wraped decals.

Using a small section of aluminum screening from a screen door, cut to size and spray with black paint.

Orient the screen so it looks like diamonds when looking at the frown cutouts. After test fitting, the screen can be hot glued into place inside the helmet to cover the open holes in the frown. Use something (other than your fingers!) to push the screen into the hot glue and hold in place until the glue cools. I had much success using a high temp hot glue gun and a small 1/2" piece of leftover ABS. A high temp hot glue gun can be bought for under 5 bucks at any WalMart.