Happily, I've liberated a slabbed coin from its case, with no damage to the coin or myself. This was my first slabbed coin and my first effort to
crack one open. It was easier than I expected, taking less than one minute. My confidence was bolstered by posts like this one (a little old, but
still useful).
I've learned that there are some differences in cases among the grading firms, potentially calling for different techniques. My case was from
NGC, and looked remarkably like the one that initiated this discussion
thread. Hammering lightly around the edges works for
NGC slabs. No special
tools are required. All I needed was a conventional hammer, the anvil (in my case, a bench vise with anvil), and a flat-head screwdriver. The coin case was wrapped in a thin dishtowel, and light hammer blows
applied on all four sides. It opened like a clamshell. The coin was then popped out of its foam insert and placed in a ready
coin flip, along with the paper tag.
If I
had one of the harder, and more brittle cases, I'd have used tile nippers (plan B: bolt cutters) to bite through the sides closest to the coin.