Does it matter what year the RX8 is?
Doesn’t appear to
Check out the guide in February’s Soft Top Hardtop (pg 62&63)
I’m expecting delivery of an RX8 stalk imminently, is it necessary to disconnect the battery to do this?
No. Most people don’t bother because the wiper circuit is isolated when the ignition is Off.
But you can if you really want to. 
Wiper fuse (20Amp) is in the under-bonnet fuse box, and it’s another convenient way to isolate the wiper stalk circuit as well as turning off the ignition.