You can open them up with a pocket knife, but with my fingers you will ruin alot of cases.
There are primer swages from practically all makers of dies. Most common use is to remove the military crimp, but they will "uniform the primer pocket" size too. Most. Buy carefully. And don't forget to lube.
The benchrest crowd really get serious about this sort of thing and you can get super critical (and expensive) tools, dies to swage or cutters to ream... Wilson, Sinclair, etc. This is not at all uncommon in foreign brass and if you have a lot, then a great investment. HAPPY HOLIDAYS. luck.