just buy a blank predator shaft and have any cuemaker customize it to match. much more reasonable and economical than to change the joint. Also changing it would devalue the cue as Robinsons are well known for that style of joint.
If you are set on having a Predator shaft, I would contact John about the possibility of taking a Predator partial/blank and having it fitted to your cue. Would imagine that he has done this before and his cues are probably so standard that you might not even have to send him the butt. (602) 996-5022 or john@robinsoncues.com
I responded to your more recent post but will use the opportunity to add something here.
I can build your shaft to mate & match with any partial of your choice, as long as it's Predator. For this application I would offer one of my Gen1 partials. Cat or no cat, your choice. PM or email please.
PS. I'm in agreement with 'Spliced', leave the joint as it is. It doesn't need to be changed nor is there any reason to.