We are not 100% sure what you mean with replace the BOX? We're sure that changing the airfilter and exhaust system will increase your speed, not sure if it will get you to 135km/h.
To our experience, the Honda PCX 150 should do 110km/h without to much problems... We also hear about Honda PCX 150 owners who without any modifications go faster than 110km/h...
I have a pcx 150 and it goes to slow 105 km/h I was told that I could replace the BOX and the bike would go faster 135km/h.
How do i buy this box I have bin to 5 honda dealer all sad they can get one but when tyey oder one it never comes to the shop. I am not happy with a bike 150 cc that goes 105 km/h