You don't have to break the "snaps" to get them off. If you look closely at the top of the "snap" you will notice the center pin is separate from the body. Use a small screwdriver or knife blade to pry up the center pin and pull it up about 1/4", this releases the three fingers on the body and the entire "snap" can be removed. When putting it back in, be careful not to break off any of the fingers and push the body down all the way. Once the body is seated, push the pin all the way down and this locks it in place.
What problem are you having with the NAV? I don't have the NAV, but I assume it is built into the radio (at least the display). I think Radio No. 1 (fuse 25 in the engine compartment is the dash mounted radio fuse.
John