There are several ways to deprime berdan cases. First of all, there's a "can opener" device that allows you to pierce the primer and lever it out. Or you can fill the case with water, put it over a firm surface with a hole to allow the primer to come out, insert a close-fitting dowel in the case neck and whack it with a hammer -- hydraulic pressure does the job.
Finally, there is a berdan decapper that has an offset decapping pin. You carefully rotate the case until you feel the pin enter a flash hole, and decap as normal.
You know of course, that berdan primers are not the same diameter as boxer primers? You can re-prime only with genuine berdan primers.