I wouldn't. I think it would ruin the look of the stone. I'm not a big fan of TV's over fireplaces anyway -- can you find another spot for the TV?

You can have a mantle attached. It should have a cleat attached first and the hollowed out very large mantle placed over it. This all needs to be done very carefully with concrete lags and the mantle attached with predrilled offset screws from underneath. Check with DIY web site to see how to do it. However the TV should not be any larger than the size of the firebox, so if yours is larger, place it next to the fireplace on a proper very wide media center credenza.