What Exactly Does "Burn In" do for Electronics?

"Ok lets say things do change after "burn in", how does any designer compensate for this, in his calibrations, measurements, tests and design????"

They compensate for this by breaking the prototypes in before they listen and measure. For example, a designer may want to try several different capacitors when building an amp to see which one sounds the best. If they want to try 5 different options, they break the amp in 5 different times. They don't do any serious listening or measurements until they break the amp in first. This is the way they all do it. I don't think you could find one company that doesn't break their equipment like this. You don't have to take my word for it, either. Call some manufactures and ask them.

I think the compensation issue is apples and oranges. Break in at the manufacturer is about ensuring it stays in spec. Changing out parts for different effect has nothing to do with so-called burn in. The same issue would apply.

I love it when people speak in absolutes. It's like when people demand. Limited life experiences are one source of this behavior or in this case, limited listening experiences.

Having a closed mindset implies one is not open to learning (hearing) something. Speaking in absolutes (or stating) demands no other course but the one proffered. It's akin to generalizing, which I do my best to avoid. It requires constant discipline.

All the best,
Nonoise

Generalizations are the source of all wisdom.

"Changing out parts for different effect has nothing to do with so-called burn in. The same issue would apply."

Like I said, don't take my word for it. Call some manufacturers and see what they say.