The decorative cover can easily be cut as needed.

If the chimney is stainless, I'd consider taking it to a metal shot to have it cut down. Stainless is pretty hard to cut yourself. I don't know how thick the hood material actually is, but if it is really thin like flashing, you could probably cut it with tin snips. Otherwise, leave it to a pro to cut.

Cutting stainless isn't a DIY job unless that cut will be well hidden. Stainless has a "memory" and is stiff and pretty unworkable compared to plain sheet metal stock or copper, etc. Tin snips will leave wavy dimples on it that you won't be able to straighten out. Even if you have an air shear, you'd need to be pretty well experienced (or plan on covering the cut with some thicker scribe molding.)

Your best bet is to take it to a metalworking shop and let them do it. They'll either have an industrial shear or plasma cutter and will be able to cut a smooth straight edge without warping the metal.

Great advice, thanks everyone (except vlord..... dude, no spamming here please. I highly doubt that Alaska Modular Homes is the answer to my hood problem!)

I'm going to look into a machine shop. I doubt that would cost much to have done, especially if my pretty blond friend (whose kitchen this is) takes it in to ask them. Thanks!

For future reference.

I just had to cut a 42" Bluestar Pro-Line duct cover down from 12" to 9" on a scribe line to the ceiling. And to make it even more difficult it was powder coated. I tried 4 methods, a cut-off wheel in a Roto-Zip, a cut-off wheel in a Dremel, a metal blade in a Bosch oscillating multi-tool, and a Bosch jigsaw with a T118A 17-24 Progressive metal blade (best method). The cut-off wheels bubbled the paint, and the oscillating saw jumped all over the place. If you try a 36 tooth blade it will get too hot and bubble the paint. However, the T118A took out nice little pieces and did not bubble the paint much, which will be hidden with caulk.

First I put one piece of plastic packing tape on the area that needed to be scribed. Make sure you use a piece of tape that will show the scribe mark in case the color of the hood is dark. Once the scribe line is made take a piece of clear plastic tape and cover the scribe line. This is important because you will be getting the scribe line wet. Now put a few more pieces of clear tape over the scribe mark, or just below it, and cover the rest of the hood with something to protect the paint while you are cutting.

Now that the piece is protected you will need to support the metal while you cut it. I will not go in depth about this other than to say that I clamped the duct cover between two pieces of wood, the piece on the back was 1/2" shy of the cut line and the piece on the front was 3" so I had room for the saw. You will probably need 2 blades and a can of WD-40. Once you are ready to cut I began with the face. The hardest part is the beginning of the cut because you need to cut through the corner. You want to run the jigsaw on the LOWEST speed possible because if you are not careful you WILL bubble the paint. I sprayed the blade and duct cover surface with WD-40 and then began the cut. With the saw on the face at the corner I came at the it from an angle tilted forward to get it started and then straightened out to get the jigsaw flat and continue the face cut. I maybe went 2-3" before I would stop and cool the blade down with WD-40 and wipe away the shavings. The best way I can describe the speed at which I was cutting is that you will hear a "PAC-MAN" noise as it is cutting. Like a wak-wak-wak noise and you will see the metal shavings popping up on top of the metal. I would control the direction of the cut with my left hand on the base of the jigsaw and push with the right hand on the handle. With hearing and eye protection, and a slow blade, I could get my face pretty close to the cut line to see what I was doing. When I would pull out the blade to cool it I would brush off the shavings to limit scratching.

The cut on the sides was a little more difficult only because it was a 42" hood and I could not stand it on end. I had to cut with the jigsaw sideways, which wasn't bad. However, the metal chips will fall on your arm and can burn so wear long sleeves and gloves.

Once I was done I was VERY impressed by how clean the cut was and there was NO chipping and very little burning! I brought it to a metal shop first, thinking that they could do a better job, but they were going to use a cut-off wheel or snips, and the snip test flaked the paint really bad so I did it myself. Now you can clean up the edges with a file and it should fit as well as you were able to cut it. Now, if you happened to have already given up on saving the paint for other reasons, like I did, you can have someone re-powder coat it for about $300. That is the worst cast scenario, unless you totally screw up the cut and you need a new cover:)