plugged in and possibly the Ignition switch on the Accessory position you should not need to reprogram anything. Make sure the lighter socket is hot when the key is out, if not then put the key in the Accessory position to get the socket powered. Always be sure to use a fresh 9 volt battery also. Also be sure to lower the drivers window to beable to keep the door closed (keep dome light and ALL lights OFF as these will kill the 9 volt battery). If you have an underhood light disable it before connecting the 9 volt and removing the cars battery. With these suggestions followed you should not lose anything in either the radio or cars computer.
Nothing is needed. Replacing the battery will wipe out the options in the radio such as oil life, light delay, and tire pressure. However these will just be automaticly reset when power is restored to original factory setting. All this means is that you will have to go into the radios settings and set your light delay and auto door lock options if wanted. The oil life will reset to zero meaning it will not tell you you need an oil cahnge for 60,000 miles which may not be true since it was reset somewhere in the middle of it's last cycle. Also the clock and radio presets will have to be reprogramed.