There is an alternate to breaking the seal. If you open the back first starting with the opposite side of the sticker you can get the rear to "Clam Open" retaining the seal.
Anyone performing these heating steps should really shroud the areas that don't need then heat. If you are not an expert with the heat gun it is easy to damage other parts. I recommend using silicone oven pads to lay over everything but CPU and GPU areas. There is also a danger of over heating RAM chips. The key here is an even increase in temp for a UNIFORM temp of chips. I have done about 500 of these and when I first started they would pop errors again after a few heat-ups and cool downs. I even broke a few heating too fast and too quick. Heres the deal, cover other areas, start with heat gun on low 16 inches away moving in circles move closer. Increase heat over course of 4-5 min.