A reformer's springs store real force, and releasing them out of order or by hand rather than with the release mechanism is how fingers get pinched hard. Always work from the manufacturer's manual for your specific model, since spring systems vary between brands.
Pro tip: Photograph the spring color-to-hook arrangement before removing anything, since resistance color codes are not universal across brands and a mixed-up setup changes your entire workout.
Watch out: Never unhook a loaded reformer spring by hand without using the release mechanism; the stored tension can snap back hard enough to pinch or cut fingers.