Hi Ken,
Sorry for the histrionics in my subject line, but I wanted to get your attention.
Please, go very, very slowly. I agree with reservist1, these birds are very fragile. If you try to wrench that bolt off before it is ready you could wring your chicken's neck.
Kaiser Bill is right, you want to use a good penetrating oil. I would be inclined to apply a few drops and leave it overnight. Now, here's the important part: Swab the area dry with a cotton bud, then apply a few more drops.
Why all this bother? If you leave the old oil on and then apply more oil, it will just pool and run off. If you swab it dry, the new oil has to 'find its gravity' again and will seek out any remaining open spaces in the threading.
I would do the oiling 3 or 4 times.
Next, if you can, avoid using pliers. You want the most positive grip on the head of the bolt that you can get, but pliers have a nasty habit of slipping and scratching pieces. Worst case, use a set of channel lock pliers that are set as exactly as possible to match the head of the bolt.
Here's the fun part: First of all give the bolt a firm but tiny twist to tighten it slightly (counterclockwise) - This is to help break the seal, but remember: A really tiny twist to the left.
Then, with a slow even pressure, try unscrewing the bolt to the right. The deal, here, is to make the pressure gentle but firm. However, don't force it.
Remember that the chicken's neck is delicate so try and support it as best you can against the torque of the unscrewing.
Now, to the chinscales: Charles shame on you! Talk about swatting a gnat with a sledgehammer! Skip the staple gun, please!
First off, get some leather conditioner like Lexol and really soften up the old leather backing, lining and strap so that they are pliable again.
You may find that the backing/lining is the same piece of leather, just folded over the strap.
From your photos, it looks like the chinscales were originally put together with heavy thread or a fine braided wire. Were it me, I would do my best to duplicate the old method.
I think that you will find that the old chinscale plates are drilled and the thread or wire passes through those holes to attach them to the leather backing.
The Lexol, leather needles and appropriate thread can be had at a horse saddlery shop.
I think Charles is right, though, about the button where the two sides of the chinscales join. Please post a closer picture of it if you can.
Well, good luck, and keep us posted.
Cheers,
Laurie
ps. Joe is right about the cockades, they look like officer's cockades and you want enlisted man's. I can help you, there. L.