'Can't help you with the 4Lo question...I don't use it.
AFAIK, you cannot completely disable the ODO display, but I could be wrong about that.
If the dealer is saying they can re-calibrate the speedo and odo for a JGC for larger tires, they are blowing smoke and trying to take your money. It's not possible...the computer only has a setting for the OEM 30.6" diameter. This is a known "deficiency". Rumor has it that Diablo is poking around to try and find a way around that, but currently, there's no solution available.
2012 Grand Cherokee Overland Summit 5.7L V8 - Winter Chill with New Saddle Interior - Nitto NT421Q