ALWAYS have a professional double check your snake sex IDing!!

I learned how to pop ball pythons by watching several YouTube videos on it, several times over, and referring back to them repeatedly while trying it on a tolerant male snake of mine.

As it turns out, there certainly is a trick to it, but once you get the hang of it, it's not difficult. Injuring a snake would be hard to do, so long as you remember not to apply too much pressure (if you think it might leave a bruise, you're pushing too hard).
It doesn't require a lot of pressure to properly pop even large snakes--instead, it requires just the right angles, and pressure applied in the right places.