Renault Laguna 02 card reader query?

I'm being told by Renault that I need a new card reader. If I get a second hand one will it mess up the electrics? How do I get it to read the new card that I have just paid £98 for? And, how do I install it, is it really as easy as taking out the ashtray and removing the card reader and replacing it or is it a bit more technical than that?