think you can buy a mk5 look front bumper for the mk4. However the rear bumper wouldnt work unless you spend alot of money due to the std mk5 R32 exhaust being centre exit, so this would mean you'd need a custom exhaust system making up, wheel well cutting out and plate welded in,please strengthing added to it. and if there is no replica bumper to fit a mk4 a standard one would have to be chopped to bits and bits fibreglassed to make it fit etc.
alot of work