If you decide to stretch your spring buy a new one right away because that will ruin it!
Magazines can be kept loaded for years, decades even and still be reliable.
Use, loading and unloading, is what fatigues springs. As long as the magazine spring is not compressed or stretched beyond its design limits it's liable to outlast you.
I'm using magazines in my carbines that are veterans of WWII and they still work reliably after 70 years.
Use them as they were intended to be used - DON'T STRETCH THEM - and you'll probably be able to teach your great- grandchildren to fire your pistol with that magazine. That is if we can keep the "gubmint" from taking all our guns away.
Regards - Al