Interesting that operators have freedom to do something about such (airline specific) ergonomic features - I pressume it would require manufacturer/FAA approval?
No, no changes to the airplane at all...only specific operating procedures.
The -500 was the first aircraft in which you could hold a optimum cruise Mach number with the use of FMS and Autothrottle.
Negative.
All SV and DL long body aircraft had Hamilton Sundstrand FMS units installed (dual installation) which accomplished the specific function mentioned.
And yes, I've flown these specific models as well.