dik, there is a provision in S16 for calculating the reduced shear capacity of bolts that are passing through unfastened shims. I don't think there is a limitation on the shim thickness as long as you account for the reduced shear capacity of the bolts. I don't have S16 in front of me right now to give you the reference.
I have been in your situation a few times - new beam being installed between existing walls, with splices required to get the beam in the room. I assume your intention is to splice the beam on the floor and then lift in place. In this scenario, unless you have some slots in your end connections, the beam needs to scrape up each wall as you lift it...and if the walls are out of plumb then you could bind up.
My process has been this - 1) get a good survey of the existing conditions 2) design beam splices without shims or adjustability 3) design each end connection with slots or some other beams of giving you 1/2"± of play - this gives you 1"± total on the span which should be enough to get your beam in place.
If you need adjustability in your end connections just to lift the beam from the floor to the ceiling, there is no point in also providing adjustability in your splices as well.