Every time you disassemble a GI mag, it gets weaker because of bending those metal tabs on the bottom of the mag tube.
It is not necessary to bend the four metal tabs to get the floor plate off the magazine. You just need to use a drift pin to depress the small tab on the bottom front through the hole and then push the floor plate off the other end. It doesn't take very much to get it out of the way to remove the floor plate.