Opinion: Don’t.
What you have works fine as a laser, even if it’s not perfectly aligned or configured. Play that ball as it lays, without replacing anything unless it stops working.
The question comes down to this: do you want to use the laser or tinker with the laser?
For the former, epoxy the shim in place and start making stuff. Lenses & mirrors are consumables, so put a set on the shelf against future need and move on. You can then make gradual, one-thing-at-a-time improvements as you understand why that particular thing would be a benefit and can measure the change to verify it’s working the way you expected.
For the latter, embrace the wholesale parts replacement firestorm and tinker away. Folks spend far more on their hobbies than you ever will, so have fun.
Onward … 