Heat bending always works (I usually use a propane torch), but you don't always want to redo or lose the original heat treatment when modding to a tool so that technique isn't always an option.
Be careful when trying/recommending a brute force technique, because sometimes the jaws will just snap off instead of bending. I've even had one or two junk pliers (that I was trying to repurpose) crack at the hinge joint as well. Not all pliers are made to the same level of hardness/brittleness. Cheap pliers sometimes snap very easily, but more often than not they will bend without too much effort. Some of the highest quality pliers are made very tough. They will often be almost impossibe to bend at all, but if you keep pushing them they will eventually bend or snap. There isn't always a good way to know which outcome will happen though.
If you heat pliers jaws to bend them, then the original heat treatment will be lost, and the pliers will be junk for sure.
As for cold bending. Yes, there is a good possibility of breaking a jaw, and this is positively a job for safety glasses. I was starting with pliers that were junk otherwise anyway. The trick is that there is most often a short plastic region just beyond the elastic region, before the steel fails, and you make the most of this.
So what I did was bend a little, and see if they sprung back all the way. If so, then bend just a little bit more. And keep adding a little bending until they've taken a set in the right position. With good needle nose pliers, they should bend quite a bit, and return to their original shape. If they snap, then they were **** anyway.
In the case of the Husky needle nose pliers I mentioned above, I had to shim the jaws at the back with enough loose change so that they were roughly 5/8" apart with the handles squeezed, and then I brought the tips together. The difference was barely perceptible with the jaws open, but when I removed the coins and closed the jaws, you could slide a couple of playing cards through the jaws with the tips just brought together.