I like KJ's idea and he certainly has more experience than me, but I do not have the tooling that he has so this is how I would do it.
I would cut the handle below Pin and heat and turn the old A-joint pin out.
Then I would turn the remainder of the old Tenon down to .623 / 5/8 in diameter. Then I would sleeve the tenon with a piece of .900 OD by .623 ID Phenolic Joint material. Once the adhesive dries from the application of the sleeve to the tenon, I would re-tap the the tenon for the new screw to clean the threads of any old adhesive "note I would use a different thread pitch that is over sized for the new screw if possible"
I would then bore my hole in the new handle for a tight fitting .750 or 3/4, then I would bore and tap a hole for the new pin in the handle. Next I would turn the Phenolic Sleeve on the tenon from .900 OD to .750 OD so that the tenon will fit into the new handle.
I have been doing it this way for awhile when I build cues with an A-Joint and it has worked very well, so I also started doing handle replacements this way. In my opinion it gives you built in Buzz protection for the tenon along with a stronger less flexible A-joint. Using this method you can still add a buzz ring if you want or other deco rings at this location. I got the idea from Burton Spain's Book on Point Blanks, and all I do know for certain is that it works.
You can also use the following method which is similar to the above method.
In this method you use a 1 inch piece of joint material and you first bore your hole in the new handle that is .750 diameter, then bore a hole in the new handle for the pin from the forearm tenon. Then you turn the piece of joint material down to the length and depth of the hole bored in the handle. Now since the joint material being used is 1 inch in diameter it should be approximately the same diameter as the forearm at the A-Joint. This allow for a one to two section of the handle that is covered by a wrap, I also have used this method while doing repairs or when build a cue with an A-joint it also will work just fine.
Hope this helps
This is ask the cuemaker section.
Not Ask The Spoonfeeder.