[nobody_special]

Keeping a spring compressed has to weaken it. Temp changes also would effect the spring in a compressed condition.

No, keeping a spring compressed should not weaken it under normal circumstances, unless it is compressed past it's design limit. Temperature changes also should have no effect, unless you put it in the oven or perhaps LN2.

P.S. I'm a physicist and my wife has 2 advanced degrees in materials engineering / metallurgy...