Most adjustment is in length of pull (distance between trigger and butt of stock). As often as not the problem is LOP is too short. If not concerned about cosmetics, a quick solution is slip-on recoil pad. However, avoid the squishy soft ones (e.g. Limsaver). They collapse too easily during recoil and can cause trigger guard to whack your index finger. Also, soft sided recoil pads don't stay put on the rifle. For LOP that is too long (e.g. shooters who are short and/or have short arms) the solution is shortening the stock. That can be more complicated. Requires some skill with shop equipment or a gunsmith.
How much to alter a gun for proper fit? Really, for a rifle it's less critical than for a shotgun used for wingshooting. However, for a hard recoiling, quick acquisition rifle used to shoot dangerous game it may be critical. The test I use for a shotgun is mount the shotgun quickly and shoot at the patterning board. If the pattern is high, the stock needs to be lengthened. And vice versa. For a rifle I would suggest removing the scope and doing the following: close eyes, mount the gun, open shooting eye and see where the barrel is positioned. If looking up the barrel (e.g. front sight is high), then the stock is too short. This is the typical misfit resulting in sharp recoil. Or the comb may be too high. The latter might require significantly altering the stock. Be aware that adding a scope will require lifting your head for acquisition. If the stock is too straight, the shooter may have a tendency to position the butt too low on the shoulder when acquiring the scope. Then recoil causes it to jump into his face rather than push the shoulder. It's why I choose low scope rings. I want to be sure I'm down on the gun when it's fired. Keeps the butt high on my shoulder. Another trick is to adjust scope eye relief so that it requires a tight fit to the shoulder to acquire full field of view. I adjusted eye relief on my heavy recoil 404J by sliding scope in the rings to where full view was automatic when I mounted the gun quickly. Marked a spot on the tube with colored pencil then moved the scope ahead just a bit, leveled, and tightened screws. A compulsory tighter fit to the shoulder is good for helping mitigate recoil for most big game situations. Perhaps not so much for dangerous game where full view acquisition is required very quickly. For those guns get a long eye relief scope and deal with recoil in other ways. Which is what I have done. New "tactical" scope should be here next week. I don't shoot the gun enough for it to make me jumpy so recoil mitigation has never been an issue. Getting my one remaining good eye bashed with the scope was the issue.