One problem is the heat shrink wraparound bandage used isn’t equivalent to the original.

Original lightning cables are wrapped with an insulator, a metallic shield and finally the outer white plastic jacket. And possibly a drain wire for grounding of the insulator.

So the simple heat shrink plastic jacket applied totally lacks the electromagnetic interference shielding capability.

My iPad charging cable has three layers frayed: the plastic jacket, the metal shielding sleeve and the plastic insulator sleeve exposing the cables underneath. How to fix them?

I did it before applying solder without issues. You may loose some cable metallic filaments though.

Here takes patience. More than half an hour for me. Use a power drill at slow speed to loosen things a bit on the hard plastic side. Screwdriver to grind and push out the cable part. More screwdriver to grind out the tiny metal clip. Finally some alcohol and more patience with screwdrivers from both sides to push out the soft plastic mantle. Careful not to brake the upper soft plastic part of the stopper. The outcome is exactly as in the picture: a neat and clean hole through it with enough space to push in the cable.

I found no need of this step. With one side off had enough space to operate.