Howdy, Pard,
The answer to your question depends on several factors:
First, and most important, what is the condition of the leather? If it is very dry, and looks like there are cracks starting to form in the surface, the answer is probably, "No!" If the leather appears fairly supple, you might be able to bring it back to life with a light treatment of Lexol Leather Conditioner. After applying a LIGHT coat (or spray-on), allow the stuff to absorb for about 2-5 minutes and wipe off any excess. Allow the leather to dry at room temperature for a couple of hours, and see if it becomes a bit more pliable. DO NOT BEND THE LEATHER AROUND ANY SHARP CORNERS WITHOUT WETTING IT WITH WATER. WET...DO NOT SOAK!
Second, if the leather feels oily to the touch BEFORE treating with Lexol, it may be "stuffed russet" (oil impregnated, NOT the color "russet"). If that is the case, you may have difficulty getting it to take water to "case" it.
The leather should be at least 7-8 oz. (7/64" - 8/64" thick) and 8-9 oz. is better. You can tool lighter leather, but you run the risk of cutting the surface if the stamping or carving is too deep.
You must wet (case) the leather with water and stamp or carve while damp. If the leather dries out before the job is finished, you need to re-wet it. Again, DO NOT SOAK the leather. Running it under the faucet for about 30 seconds should do the job. Smooth off any water drops or excess water to avoid watermarking.
Pick up some books on leather carving. Tandy/The Leather Factory has a number of good ones on the subject.
Practice on some scrap before working on the "good" piece.
Good luck with your project!
Ride easy, but stay alert!