I would recommend the op find (if he can) a competent cue repair person unless he has extensive wood working skills.
I’ve sanded so much in my life my fingerprints are destroyed. While getting a CC in Illinois they were going to refuse my application because they could not get ‘acceptable’ fingerprints. After five attempts they called the supervisor out.
He looked at the mush and asked me what the hell happened to my hands. I told him what I did for a living and he told them to pick one and give me my permit. Lol
I’ve done my own shaft reductions and done some for others as well. If the OP is going on his own he needs to start slowly with a reasonable grit knowing every time he puts paper to wood he will be taking something off. Then he better know how to reseal and finish the shaft afterwards. It’s not just about the grit of paper!