Good idea to post up an ad! Nope can't adjust cluster for tire size. There isn't much you can adjust/tune, i think it's mostly made to monitor and diagnose not really tune and play around with the performance of the machine
This is what you can do with the diag-system: you can reset the dps torque offset, reset the tps, program keys, change display message, reset "maintenance required" message, you can activate the fan, fuel pump and fuel pump pressure relief to test, theres a "WOW test" (lol that's what it says on the program) and it makes your cluster go ape ****, so im guessing it's doing a test of some electrical systems? Don't know. You can also change the language on the cluster and change it from metric to imperial.
You can monitor your rpms, engine temp, battery voltage, intake air temp, intake air pressure, throttle opening, can also check error codes and you can clear them also, and the last thing pretty much is theres history of the machine, like max rpm, min. rpm, bunch of graphs of the history of your speed and rpm and other things.