I just shared one of my custom iTunes Radio stations to a friend via email. What happens when they access it in iTunes? Are they getting a read-only instance of my station, a read-write instance, or a one-time copy of my station at the time they first access it?
From the Apple website:
With iTunes Radio, you can easily share stations via AirDrop, Mail, Messages, Twitter, and Facebook. The stations you share continue to change as you tweak the mix, so your friends can listen to music that adjusts with your evolving tastes. Show off your favorite stations, or tune in to your friends’ to hear what they’re into.
So, it appears to mean that they're getting a read-only instance of your station, that updates as you update it.