I don't know nothing about nothing,
...but I slept in a Holiday Inn last night & took a quick look at diagrams on John Deere parts website and .
It's hard to see what's going on across multiple diagrams, but presently does your PTO (mower on) lever engage pulleys on the deck that tighten the belt?
And when mower is off, does the belt just slips around the idler puller that's at the bottom of the engine?
So essentially your looking to replace item #18 on "power train/Belt Drives and Idlers page (P/N: GY20140) ?
John Deere - Parts Catalog
Don't know how easy it would be to replace this with an electric. You want to make sure electric clutch matches the bottom motor shaft, that the bottom motor shaft is long enough. The tricky part is
I think electric clutches require a fixed "rod" that doesn't spin extending down from the tractor so that the bottom part of the clutch assembly (where the wires connect to) doesn't spin. You have to accommodate this.
If you did add one, it would probably be easiest to leave your regular mower PTO in place and just leave it on rather than reworking the pulleys on the deck.
Why do you want to do this?
I miss the old pulley operated PTO of the Cub Cadet I had where you could ease the mower on instead of slamming it like electric clutch does (Although my mom's Honda mower has a pulley system on the deck that can't be eased, just reaches a certain point and slams in).