I have cut two stocks down to change the LOP. I used my DeWalt 12" chop saw with a fine-toothed carbide toothed blade that I bought just for this purpose. I taped up the stock to deal with chip out and I should have wrapped it with more than one layer of tape as I did get a little chip out and I did go slow. But walnut can be difficult.
My first one cut was a high-end shotgun, and it did give me a little pause, but it turned out perfect.
For yours I would be at least thinking about cutting it out on my band saw and follow the current radius.
Good luck
Fleener