I would replace the pads since the one ripped, just to be on the safe side. You're also right about the twist method being unsafe, it's better to use heat and gently pry with something like a flat screwdriver.
Oh, I did replace the thermal pads. I mentioned the new pads in the text somewhere, but didn't include a photo.
When I did the mod, I first just used the Gamecube to get it heated up, then disassembled it and removed the heatsink. I hate to admit it, but I did rip some of the thermal pads but they seemed to smoosh back together okay and I didn't have any alarming temps reported by Swiss (though the Swiss temp reporting is quite inaccurate). I've had zero issues with stability and have since done the blueretro internal mod.
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