Sorry for what may be a dumb question, but I have a ten inch cork grip on the way that I am pretty sure I am going to want to shorten a couple of inches. It doesn't seem like rocket science, but I have never had a reason to do this before. Can I use a fine toothed hack saw and a mitre (or miter if you will) box to do this? One end has a tenon for the butt cap, so of course I will be cutting the end up against the reel seat.

Yes.
If you want to save the butt cap, I cut a parting line with a jewelry or small dovetail saw and then it will often twist off or need a small amount of heat. Then trim as appropriate (leaving a new tenon if you wish) and reepoxy.

Ernie,
There is no need to guess, just spin some arbors from masking tape on the blank and install your reel seat and reel in a few places till you are comfotable, take your measurement and build you grip to it.

He is talking of shortening a grip on an existing rod, I believe. I had to do this when I was first starting building and I just cut the butt end off and refit a cork butt piece on. I didn't even use a tenon, just a flat epoxy-glued joint, and now about 15 years later it's still in good shape. I don't use rod holders, though. One can easily fit a butt piece with reinforcement of the blank, just jut down to the blank and remove the cork. Then cut the blank, leaving a short piece sticking out that will go into a hole in the butt piece.

I would not recommend trying to take a section out of the reel seat end. Then you have to fit a splice the blank. Cut off the end. Much easier to deal with.

I think he’s talking about shortening a pre made cork grip that he has ordered. So an important question is whether the grip will be used on a spinning or casting rod. Many of these pre made grips will have a 20 mm tenon on the butt end which fit a specific size butt cap whose OD matches the OD of the grip end. So cutting from the rear end of the grip may require finding a butt cap that will match the OD of the cut grip. Since this can be a PITA, it may easier to trim from the front of the grip. However, if it’s a casting grip, they usually come with a 24 mm tenon on the front end that fits the casting reel seat’s inlet with the ODs of both the grip and casting reel seat matching. So cutting from the front end of a casting grip can also cause some problems with fit and finish. If a spinning grip, they usually don’t have a front tenon. so it becomes easier to cut from the front of the grip. This because they can usually be trimmed without affecting fit and finish with the reel seat very much, unless you are using a very large reel seat. A straight grip is easier to trim than a tapered grip.
For cutting grips I use a fine toothed Xacto razor saw, make sure you make a square 90 degree cut.
Norm

Yes, Norman, you are right in your interpretation of the question. I didn't read it carefully enough.

Thank you all for your replies. Norm was right in his interpretation. But...does everyone usually answer questions keeping whoever asked it in the first place in the "third person"? :-)

I cut my cork like the Flexcoat people do in their video, but not everyone has a power wrapper.

If you have a shaped grip coming that matches the contour of a particular reel seat, then you will need to cut from the butt end of the grip.

Also, many grips come pre shaped to have a nice contour for the best grip.

Again, if that is the case, only trim from the butt end of the grip.

If there happens to be a tenon cut into the grip of a pre-shaped grip, simply cut as much of the grip shorter, and then, cut a new tenon into the end of the grip, as I mentioned earlier.

Best wishes.