Can I install a body kit bumper and grille on this car?

It would depend on the kit and who makes it. Most kits are sort of universal when it comes to a particular car, so a kit to fit your 2003 won't be an exact bolt on, most will take a bit of fitting and care to make them fit really good. I would start by seeing what kits are out there that you like and will fit your car. Then decide how you want to attach it, some mount to the factory mounting, others will be a slip on part that glue or is taped on. Then test for it and make any changes needed, be advised that many of the real custom cars you see may not use a kit for that car but use parts they want to use and cut and reform them to fit the base car.