yea, DEFINITELY do not use regular torx. also make sure your hands are firm and steady. i stripped a screw with a torx, and had to slice through the metal case to replace my battery. total nightmare.

about the sim tray mod, you may find that it will be necessary even with a new case. the case doesnt do much to hold the sim tray in place, its actually the mainboard. you could always order a cheap replacement sim tray, and your carrier will replace your sim card, often for free or very cheaply, if you 'lose' it.

that being said, unless you cut the gold metal, you wont damage the sim card. ive done this to about 8 sim cards from three carriers, and its always usable in other phones afterward, even in microsim adapters.