I have personally never seen a cutlass bearing being replaced without pulling the shaft. Even if the yard is able to do so, why would you?
The bearing area of the shafts can't be examined unless the shafts are removed. If your bearings are shot, you may also have worn shafts in the bearing areas. The shafts are subjected to a lot of wear in these areas, especially in muddy or silty water.
The shafts can also suffer from the dreadful crevice corrosion, especially in the stern tube area due to low flow and oxygen starved water. I have seen more than one shaft snapped in two, caused by pitting and worm holes due to crevice corrosion.
If your shafts have any problems of this nature it is highly advisable to deal with it while changing the cutlass bearing than having a shaft snap while out cruising, your choice.