If you add an external voltage of 12 v to the 5v arduino bard will the board fry and is there a way to do this with out fying the board.
Yes it will suffer from that.
An Uno board as well as a lot of other boards (meaning: not all) have a so called barrel jack.
You can supply 12 volts to it without trouble.
It will be sent to a regulator that "transforms" (or rather reduces) the voltage to the 5 volts needed by your Arduino.
The 5 volt pin is just for that, 5 volts and nothing else.
I use a motor shield. This allows me up to 24v of ext. power. I currently have one to control a stepper motor in my robotic arm. The stepper takes 12v.
If you provide 12V it must go either to the barrel jack or to the Vin pin.
Touch any other pin with 12V and instantly dead Arduino.
Mark, unfortunately I left the jumper on the motor shield and did just that. Costly mistake, but your right, never did that again!