I must have at least a dozen carbon shafts of various brands that have been lengthened by up to 2". Never had one fail and I shoot alot. Believe it or not, I even miss from time to time (very rarely mind you).
and have hit roots, dirt, rocks etc with most of these shafts at one time or another. No structural failures to date.
I'm sure some will disagree but if you only need to add an inch, a 2" aluminum external footing with an insert will add 7/8".
I install an insert in the carbon and file the lip flush with the outside of the shaft.
Then overfoot with the 2" aluminum so that the base of the insert in the aluminum footing is seated tight against the insert in the carbon.
You might try making just one up and torture testing it before selling your shafts and buying more.
Ron