I have a 2007 400ex. The front fender has a broken mount but it will still work. However I see it as an oprotunity... I like the older style (99-05) front fender better. Would the older style fender fit and properly mount onto my newer style? If yes that still leaves the matter of the headlight. Would the older style headlight fit onto my 2007 along with the older style fender?

 

People that upgrade with the older 400's are able to run the newer style hood/headlight you have, they just have to weld up mounts. As for the rest..... I think the fuel tank plastics are differant, i couldn't see it working.
I'm not much on the old style bug eye headlights personally

I'd see this as an excuse to get new plastic!!
Maier Mfg Front Fender 117370 for Honda TRX400EX Sportrax 2005-2007 | eBay

lots of cool colors out there