Once you know what changes you need to make the your incidence, rather than shimming you can bend the tail boom.

1. Place the fuselage in a vise.
2. Hang a small weight from the end of the tail and heat the boom with a heat gun.
3. This will introduce a gradual bend.
4. Periodically check the amount of bending with a straight edge ruler placed along the boom.

If you ever need to straighten it, just heat the boom without the weight attached.