Then what do you do, throw'em out and buy new ones?
replace the spring with a new one.
I could go into a lengthy discussion on physics, spring steel, deflection vs the point of permanent deformation, but I'll sum it up as this: a magazine spring is designed to work within the range of "empty" to "full" if the spring is old and worn out, taking the magazine apart and pulling the spring back apart does nothing,because as soon as you load it back full, you've compressed the spring back to where it was before.
also, USE is what wears out a spring. meaning the transition from empty to full back to empty in a magazine. a magazine left empty and a magazine left loaded, the spring will not "age" and the loaded mag, the spring will not "deform" or "compress" and a magazine that's used on a range, every day, constantly being cycled back and forth from empty to full will wear out the spring in short order.
Think of a pop can. crease it down the middle. bend it one way. leave it there...nothing happens. bend it the other way, leave it there...nothing happens, but when you bend it back and forth over and over, eventually the metal cracks.
THATS what wears out a spring.
anyway, if a magazine spring is worn out, there is no band-aid. simply replace the spring.