The single handle stations are typically electronics controls. The handle has an electronic cable to that goes to a controller. Which in turn handles both throttle and transmission. There's usually electronic cables from the controller to separate electric actuators that interface with the existing engine and transmission systems (typically by mechanical cable).
It's do-able as a retrofit provided there's enough room to properly mount the various pieces. But it's going to be pricey, in both parts AND labor. $20k is probably your starting point, budget-wise. And it's something best done by an service company that's done them before as there's a bunch of fiddly details that have to be dealt with. All of which potentially mean added costs and potential delays. Adapter for x to y, bracket(s) to fit various areas, etc.
The two important starting points are the transmission and engine and then it's working back from there. While doing this it would probably be smart to consider how any thrusters or the windlass would also be integrated. Wireless remotes options exist and a job like this would be the right time to integrate them, if so desired.
The larger question is will it be "worth it"?
From ease of use, sure, they're a welcome improvement over clunky cable controls. Lots of potential options like changing transmission slip (trolling, express, cruise) and easily adding multiple stations (lower, flybridge, cockpit) or even integration with GPS for station-keeping.
Properly maintained cables are certainly going to have less components to fail, which I'm sure the Luddites will chime in about. Less electronics, less reliance on available battery power, etc. Those are all correct points. But then you're still stuck with a very rudimentary controls.
There's also the issue of pouring a bunch of money into an option that's not going to have any affect on resale value, long-term. And if they job isn't done *perfectly* you could well be looking at a decrease in resale value because of it. DIY hacks are not something a surveyor will look kindly upon.
Sometimes folks hemorrhage a bunch of money trying to make an imperfect boat "less so". When they should probably just look for a boat that already has "everything they want".