When maf scaling is stock and spot-on...

Is my understanding correct that if a maf scaling (stock injectors and filter housing) is correct and spot on, my commanded AFR will also be correct even if i do not use AFR gauge on open loop?

Also, i can upgrade full exhaust and turbo without the need for tune as long as my maf scaling is accurate? Well of course, as long as i am not overboosting and not maxing out my maf.