RE: Replace the Cylinder or just the ring on a Saito rebuild?
If the engine is to be disassembled, and you have the bearings and ring handy, I just don't see the point of loosing the opportunity to change all stuff.
As have been said, the cylinder wall has a chrome plated cover, I do not know how thin or thick it is but I have done all my rebuilds with out sanding the walls, they are usually clean and I just clean the cylinder and lube it with 2 stroke oil.
Take care that the new ring seat at the same position as the old ring and that the piston stay in the same positio too.
Good luck.
Alfred.