Changing left rear disc- how to needed

My left rear brake must have picked up something very hard or the pads have something in them very hard that deeply scored the disc so I'm going to replace it. I bought the disc from Subaru and Hawk Street performance pads to install. Once I had the wheel off I discovered that the nut that holds the disc to the axle has a crimp shoulder pushed into a slot on the spindle. How does one get the crimp out of the slot? Should it be ground out with a Dremel? No matter how it comes off I assume a new nut is required for reassembly?

thanks in advance for advice

Stop!

That nut is for removing the axle. You do not need to remove it to remove the rotor. To remove the rotor you need to first remove the caliper. Then you need to go to the back side of the dust shield and remove the little rubber plug towards the bottom. You will then be able to reach in with a small screwdriver and turn the start-adjuster turnbuckle that adjusts your parking brake. As you loosen this nut the parking brake shoes will clear the inside lip of the rotor and it can be removed.

Upon replacing the rotor you will need to adjust the parking brake back so that the shoes are just contacting the rotor.

Thanks a bunch.

I completed the R&R yesterday. All is fine.