I would be inclinded to change both fronts as the rears don't do much other than check cat effeciency. You can get the O2s for about $100 if you shop around. If could be a bunch of other things too (bad wire, bad plug, stuck valves etc. etc. etc.) If you have 100k on your O2s, replacing them won't hurt.
I am not sure about the PROM update, but you would need to go to a dealer or an independent who has the scan tool to do that.
*not legal advice*