Combo Action Button

[Reynhart]

I'd love to know your definition of the word "change" because fusing two buttons on separate slots and onto a single slot is exactly the literal definition of the word "change".

One definition is easy. What you can already do by using a macro is not a change. Because yes, if macros didn't have the issue of not queuing properly, you could already do the ability switch from Fire IV to Blizz IV, combo step to the next combo step or Blood Weapon to Blood Price...
Before they did it for Fell Cleave/Inner Beast and Decimate/Steel Cyclone, that's what my WAR Stances macros were created for...