If you have cases that are just charged with no bullets, empty out the powder. Remove the decapping pin from the die and just use the sizer on the neck to true it up, a little dry neck lube doesn't hurt either. You don't have to cycle the full length if the brass otherwise meets chamber specs. Chamfer the case mouth with the case mouth end down so brass shavings don't get into the case. If the bullets are already seated, pull the bullets with a bullet puller and follow the above instructions. Chances are if the bullets seated OK the first time around, you don't have a problem but doubtful they'll be exactly what you are looking for. Unless you are just plinking and not looking for accuracy you might be able to reuse the old bullet if it isn't scarred up or burred too badly.
Primers are relatively cheap, no way I would reuse a live primer that has been decapped. Throw them in a bucket with some old oil or the like to kill them off.