[size=1][red]NO[/red][/size=1]
The hole for the powercord is at the back and bottom of the safe for several reasons.
First, the fire-resistant safes have heat-expanding tape around the door, to seal up the safe when there is a fire.
Second, air expands when it is heated.
Third, heat rises.
Fourth, if you plug that hole, expanding air (see #2) from inside the safe won't be able to flow out at the bottom, where things are cool (see #3), thereby building up pressure inside the safe and causing the seal (see #1) to blow out wherever-the-hell-it-feels-like-it. Which is NOT what you want, since if it blows at the top, hot air, not to mention water from the firefighting, can get in.
So, don't plug the damn hole up. Think about it. If they'd wanted you to plug up the hole, they would have told you to do it in the instruction manual, right?