Yes, leaving them in the foil is the best way. Of course, all blades in the foil must be exactly the same thickness. If you move swiftly and get the blades between the plates fast, the transformation will be locked in. Once the color is gone from the blades, you can quickly open the packet and get the blades out-then press them again.
I check them for straightness before I re-press them.
Don't forget to temper them while they are still quite warm.
Stay Sharp,
RJ Martin