I'm not sure which mounting system you're using. With the addition of a shim this will help with elevation adjustments. So, if your smith said he might shim I'm guessing he ran out of elevation adjustment? If he ran out of windage you can change to a windage adjustable mount assuming one is made for the X-Bolt. The mounts I've seen for the X-Bolt didn't allow for windage adjustments in the rear mount. I will assume Leupold makes this kind of mount for the X-Bolt. If in fact windage adjustment has ran out using a shim will cause no adverse problems. Just make sure the shim is made of metal and not plastic. The plastic shims deteriorate over time and the metal ones will not.