Some things you should know:
1) Your CPU will not make your case any less hot. It will still put out the same amount of heat. The temperature of the CPU will be a little lower, likely, because it will more effectively get that heat out of the CPU and into your case.
2) 60-70c is actually pretty low for that CPU. Many have theirs running at 80-90c, which will not harm it either. Throttling is at 100c and shutdown to protect the CPU is at 130c - you're still almost 60c away from shutdown temperatures.
3) DO NOT USE LIQUID METAL WITH YOUR HYPER212. Part of the baseplate is aluminum. Liquid metal (which contains gallium) will destroy the aluminum. It will crumble and fall apart. Google it, YouTube it. It's safe to put under the heatspreader if you do delid, because the heatspreader is copper coated in tin, but absolutely do not ever let it come in contact with aluminum.
I honestly would not recommend you do anything to it. Temperature is just a number until it causes throttling, which it is clearly not in your case. Lowering it will not do you any good. Your CPU will not dump any less heat into your case or room, you'll simply have a lower number.