Okay, I just looked back through the thread. In the first picture, the hp gauge is reading the same as the post-refill picture. That tells me that the high pressure gauge is busted.
I'm still not sure what's going on with the hissing. But, yes, it's probably safe to remove the regulator. If you want to wait on venting the cylinder, I'd bring it to a homebrew/hydroponics place, or a good LFS, and have them test the cylinder pressure with one of their gauges. And, in the meantime, I'd order a new high pressure gauge (probably less than $20 shipped), or see if a local shop will sell one.