I have inherited several firearms with leather wrap/lace recoil pads, shell holders, and risers. Seems all of them had some discoloration but the accessory had been attached 30+ years. `Without knowing the type of finish process is used on the stock nor the type of tanning process used on the leather you could not be certain. Best thing to do would be to attach the accessory when you need it and remove it when you store it.
The Greatest Enemy of knowledge is not ignorance,
it is the illusion of knowledge.--Stephen Hawking