You must be doing it wrong. Omnas are the easiest amps I've ever opened, no filing, no paper towels, just used my hands on 50 amps. Find the white dot on the amp, it should be facing you, and the notch in the neck pressed against your index finger. Then just press at the top with your thumb, not much force at all.

I've used a lot of different HG amps, omnas have never broken and never needed a file or anything, they snap very very easily.