Is this something anyone has done or is a practice? Like say you have a stock that you like the general make up of just it's too "fat* is there a way a guy could say, plane it down to narrow it ?

I did one this spring for a neighbor. I thinned the whole stock. There was enough wood on the forend that I put a snabble tip on the end (which he requested)! If you would get a fine tooth rasp and some kind straight edge you can thin your stock down.

… get your angle grinder out and get after it lol

I did an MAK-90 thumb hole stock , didn't want to R922 it so I made the thumbhole actually fit my hand then re-finished it.

rasps and sand paper

Have you considered plastic surgery, or at least tried to stop smiling so hard while you are shooting.?
I was tasked to train a new shooter the fine art of precision shooting. Our 308s are equipped with heavy laminated Monte Carlo stocks.
This ole hand had a jaw like a banjo, and his eyes were so close together you could poke both of them with one finger.
There isn't enough wood in a telephone pole to carve out a groove for that guy.
He just had to learn how to shoot lop-headed. It took him longer than most that I have trained, but he did become an excellent shot over time. It's all about doing everything exactly the same on every shot.