I took my factory GT emblems off some time ago, and installed 1968 GT emblems in there place. The entire switch out took less than 20 min. Take a credit card type piece of plastic and slide it under the GT emblem as you slowly pull the emblem away from the car. The factory emblems are not very rigid, so take a little care with them. I had no problem at all removing them and actually have them stored for safe keeping. This method of removal, did not harm the paint at all.
If interested the 1968 GT emblem are metal, that I installed just like the original. The mounting pins were removed and 3M tape used to afix them to the car. I have had them on now for almost a year and no problems. They look great and really go with the car.