I'll try my best 
A considered opinion is fine, but back it up with fact, I don't tend to take a lot of notice of spurious comments without explanation.. One fact being that the AP box will handle what a 1275 MPi will sling at it (agreed this box is a little different from the earlier box).
Let's be honest - no gearbox job is a DIY garden shed job - you need to know what you are doing, and to have the right equipment to do it with. How many jobs you get are putting right munch ups because someone didn't know what they are doing?
It's wrong to say that a mild tune will compromise the driveability of the box - it won't. If you do something silly like stick a wild cam in it that needs a high idle and kills low end torque then commons sense says it will be detrimental to driveability but it won't break anything - you'll just have all the torque in the wrong place to take advantage of the converter.
Mod to increase low end torque and top end power and you'll be just fine. These boxes are a compromise for no either reason than oil quality - they'll take quite a bit of mortgage slung at them
