The way I explain it is that I "blade the pizz" out of them. I think it was Braz that was very surprised when he got one of my calls and saw just how far I blade them.
Like Al said though, you CAN, and I have SEVERAL times, gone past the sweet spot, and then the reed is junk. This happens when you bend a metal reed PAST the point of the right lowe tone vibration that you need. Go slow is the best rule to follow. If you go slow, you won't go past the spot. I tend to go too fast sometimes on some projects.
You can definitely try the reed in the call both directions. I prefer the bellow to suck air across the reed on the small bellow kit, and to blow across the large bellow kit. Others prefer for the small bellow to blow air across the reed.
You blade the reed with a razor blade, while holding the base of the reed in your hand, being careful not to pop the actual reed off of the metal assembly. You're permanently bending the metal reed up is what you're doing. The mylar reed that's under it also needs to be bent up, but not at near the angle as the top metal reed.
If you have the double metal reed for squirrel calls, it is MUCH easier to mess up the blading process, because you'll bend the bottom reed too much too easily.
You'll want to test things out as you go, and you may blade a specific call up to 5 or 6 times until it hits the lower tone that you'll want. I'm to the point now where I go to a specific level, and go from there. One out of every 10 I'll get right the first time, the others still take me about 3 tries to get the tone I'm looking for.
So, while you're trial and erroring this, you want to be very gentle with the reed, as to not ruin it taking it in and out of the call. This is EASILY done! You need to get one of those white Bic pens, either a click top, or a basic one, and remove the guts from it. Just make sure the white tube left as your tool is smooth on the inside, no threads. This tube fits perfectly over the reed, and allows you to push on the rubber bushing to remove the reed and bushing all in one. There's no need to remove the reed from the bushing while you're doing your trial and error tuning.
HOPE THIS HELPS!
I'll see about getting a picture up in the next week of what I mean by "blading the pizz" out of it.
Parker