870 tube extension

Try and stay with me while i explain this, i warn that i am just getting started so the terms and words i use to describe my problem may be very incorrect.

The newer models of 870 express shotguns have two prongs bent in at the end of the tube to catch the plastic piece that holds the sping in. The problem with this is that when you purchase an extension those prongs must be removed so that shells may slip past them. What is the best way to accomplish this? I was going to try and just bend the prongs in with pliers, but the tube metal is more sturdy than i had originally thought. Because of this any attempts to bend the prongs put the threading at the end of the tube in jeopardy. If anyone has any insight or advice it would be very appreciated.