I want to change batteries in my 03 Crown Vic and I am wondering if I hook up the dc/dc cord if this unit will feed current back into the car thus retaining the computer settings and the radio station settings?

This actually quite a good trick to provide an appropriate (eg. charged) 'alternate' DC power source to maintain the minimum voltage and current to hold the computer, radio and alarm setting for your car while swapping your car battery (I have myself used 2 small 9 Volts batteries in series via alligators clips for this purpose): just make sure that it is connected on the correct side of the cables where voltage and current will be maintained after the main car battery is disconnected!
Hope it works for you and have fun!