Lots of people have modded them, though few have gone all out. PHEV is the ultimate mod. Of course it also costs the ultimate amount.
Here are a few mods I did to either of my Prius'. I had a black 04 before my current grey 04.
http://ecomodder.com/forum/showthrea...ock-19294.html
EV switch
block heater
PHEV kit - this one never really worked out very well