Why not doing the full A9LH install instead? The time to do it is about the same and the benefits are even greater.
You can do the part 1 for Decrypt9, either with MSET or with Browser (if He has one)
Make a backup of both Sysnand and Emunand and copy all SD to a folder on PC (this will let you have the Nintendo 3DS folder that is attached to the Emunand and Sysnand).
After the backup, instead of doing the 9.2 CTR transfer, do the 2.1.(Part 2 of the guide).
Then in part 3, just restore the Emunand to the console and the Nintendo 3DS that goes with it and He'll have the console as it was with A9LH.
Easy as that.
But, yes, you can do the 9.2 and keep the HBL+Menuhax just the same.
Just make sure your booting on Sysnand and launching Decrypt from there before doing the 9.2 transfer.
Also, I saw somewhere that if the transfer errors, don't reboot. Just try the transfer again.