Hi guys. Been a longtime reader here although I don't post much. I'm a casual builder and have done 20+ rods for myself. Need some advice.
I found an old broken factory spinning rod that has a beautifully done handle and reelseat. I have an idea to preserve this handle by cutting it off just in front of the foregrip and inserting a new blank (with a diameter slightly smaller than the original)all the way thru to the butt and gluing it permanently. I know this is a lazy man's solution but I also know that with my skills there's no way I can replicate that handle. My question is - will having 2 layers of blanks in the handle section affect anything? Weight will definitely increase a little but we're talking about 13 inches of a thin walled graphite spinning rod here. Would sensitivity be affected by the extra layer of graphite and glue to the extent that I would notice it? Any other downsides? Tks!

Yes to all the above. Some sensitivity will be lost. Some weight will be added. But, it'll still work. You're looking for practical differences and these will be slight.

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Measure the inside of the blank after you cut the old rod off. Next order two brass rod ferules that will fit inside the blank. glue the long female or bottom of the ferule into the into the handle. Add some rod blank to the back of the joint before you slide it in, if you feel it may need further reinforcement. cut the blank you wish to install in to the grip to were it will fit in to the other end part of the joint. Why two ferules, why stop at just one rod. Were is it written that you cant change your mind or further your options . You may fit several cast off rod of differing lengths and weights into a single handle. Old broken rods often find there way to the guy down the street who fixes rod for the neighbors and friends. The bone yard is a gold mine at times.

Linus,
Yes, you could do that.

However, an easier way to use the same handle and reel seat would be to obtain a new blank to your liking that had a butt section that was a bit larger than the size of the blank coming out of the front of the handle.

Then, cut the salvaged handle with protruding blank about 4 inches in front of the handle. Then, by trimming the new blank a small bit at a time, - trim just enough off of the butt section of the new blank so that it fits snugly down on the outside of the protruding blank coming out from the salvaged handle and blank. When you have it aligned to your liking, mark the orientation, and then glue the new blank on the salvaged handle and blank. No added work or inserts will be required.

Then, go ahead and add guides and thread wrap and enjoy the new rod.

Good luck