Re: Switching to TG while maintaining MG skills?
I think you will just need to practice both, if you want to be proficient at both.
Just a little personal history - I started with traditional grip nearly 40 years ago and played it exclusively to start with, including several years in drum corp. Later, (and I don't remember exactly how many years later) I started playing matched grip because I was playing rock and used a bigger kit.
Fast forward - these days, I play matched as my main grip, but my left hand has never developed to the level my right hand has. And despite playing trad only intermittently, it comes back to me in no time, and I am still faster and can still play many things trad that I can't matched.
For reasons I can't really quantify, if I were starting today and I started with matched grip, I would play matched and stick with it only...