What does a uncentered speaker sound like if you refoam and don't get the cone centered.

It will throw off the proper pistonic motion, which is never really perfect to begin with. In other words, the sound wave propagation will be distorted.

Try pressing with thumb and middle finger using both hands,basically four corners of a square on the cone ..equal pressure on the four points ...down with light pressure moving cone in and allow it to move back...do that a few times and if you feel rubbing its messed....the rubbing will sound like distortion  when audio is run through it....if you redo it again use shims so coil is centered.

I can not get the center dust cover off.. I tried a very sharp razor knife and its not cutting it. I can just cut it off but I wanted to reuse it. Too scared of cutting the cone.

The cracking sound you’re hearing is the voice coil banging into the magnet and pole piece. The voice coil gap is very tight. Two things hold the coil in alignment- the spider, and the surround. The spider is the big accordion looking thing behind the cone. The surround is what you messed up. When you glued the cone off center you also caused the coil to be out of alignment. It is okay and has enough clearance, until it starts moving a lot with powerful bass. Then it scrapes and makes that sound.

If you haven’t abused it too much already you might be able to cut the surround and re-glue it properly and save the driver.

Do not cut the dust cover. Behind that is the spider, the one thing that is still in the right place. Lose that and you are screwed. Whoever said to cut the cap is telling you how to destroy it for sure.