The rectangular-wound wire style spring used in the 527 magazines doesn't lend itself to easy "re-tensioning", since it needs to maintain certain geometry for proper feeding.
You may have to clip a coil off the bottom and see where that gets you; or heat a lower bend to take out the temper.
But take measurements to make sure it will still have enough length, and be prepared with a spare, before hacking it. Once you go too far, the spring is junk.
If there is a *skilled* gunsmith in your area, they might be able to fold up and temper and flat ("accordion") spring for the application.
Yes, springs are easy to make and there are even 'easy' ways for idiots to temper them. But the average modern gunsmith doesn't even understand what a part's function is, let alone how various parts interact. So they can't be expected to understand how to keep a follower level in a magazine. Skill and brains are required.