Q About New Rims ...

You can adjust that through a Speed-Cal. I believe the tuners can do that too though. I've never messed with a tuner.

just get a hand held tuner, it can adjust for tire size and help with performance, nothing else u need to worry about really

If you run a lower profile tire the overall diameter of the wheel/tire combo
may be the same anyway.

As stated above, usually you don't need to do anything because the diameter is the same. The rim gets 1" bigger in diameter and the tire gets 1" smaller in the sidewall, unless you specifically order a larger diameter tire. For instance, I ran 275/40/R17 on my stock bullets. Then 275/35/R18 on my 18" rims. Actual tire diameter does not change, just rim and sidewall size. But you can put a 275/40/R18 on there and then it would be close to 1" taller tire that would require speedo adjustment.

Found some pics. It's not perfectly clear by this picture but they are the same size even with different rim sizes.