It is a family heirloom that you seem to regret having because of bad experiences with it in the past. If my thinking is correct, then pass it along to another family member who might appreciate it and go buy what you want.
+1
I'd say this it the best choice, just make sure who ever gets the gun knows the rules.. keep it stock, take care of it, keep it in the family.
If this is not an option, Then the next best option would be to buy another gun, keep this one stock, shoot it on special occasions.
Last option would be to get a different stock so you can shoot the gun, but keep the parts so you can revert back later, changing the stock is not a radical modification.. it should be completely reversible.
Ideally you would keep it as it is, but if that's not an option I don't think it's TOO big a deal.. after all it's your gun now.. and it's still a family heirloom.
Imagine you take it hunting and it gets a scratch, so what? it just says Wildernesshunter owned and used it, look at it as a enhancement of it's family history.
You'd have to look at any modifications in the same light. and what you're purposing is not going to damage the gun.