The installation of the Ixrace MK2 exaust will reduce greatly the weight of your Honda (about 5 kilograms). It's road-use legal in Europe with Euro4 norms. It's MotoGP design looks much nicer than the OEM and provides a great sound to your CB650R !
It's strongly recommended to change your header gaskets when changing the exhaust.
It's not needed to make any fuel injection optimisation as the Ixrace exhaust has a O2 sensor plug in order to keep your motorcycle works just like with stock exhaust.