You have to use new wires , because it's totally different. No programming involved in that. Check here :
http://wa4ekg.home.att.net/996mods/sidemarkermod.html
I tried to reprogram my car but the only difference in the end was that I had a 24 hour clock instead of AM/PM.
When they told the alarm to be european instead, it finished working so I had to program it back to US Spec.
The tripcomputer can't be changed to metric if you have it .And the Speedo is just to turn one of the nobs for a few seconds (but you probably know that)
Good luck!