I would imagine it would be very costly to do so
Why not De cat the car?
Ive seen a 3.0V6 (es9j4s) produce upto 10+ more HP & torque with its cats removed. It still passed its MOT due to the fact that it still had its Pre cats installed.
With 2 petrol and 4 Diesel engines that are faster than a 2.0 petrol already available in a 407 it would make more sense to obtain a 407 with one of those engines already fitted. As an added bonus they all come with bigger brakes and slightly altered track to manage the extra grunt.
Taking one of the slowest models available then then tuning it instead of just getting the fast one to begin with seems a bit silly.
Agree to an extent, but in the end, even 240 bhp is nothing these days if you're into car tuning, so when starting to modify things a lot problems will arise even though you got the fastest standard car avaliable.