If you use android app to control WC8, that allows to rename its IO. However, web gui has no easy way to rename it, because not only GUI name being seen on screen, but also in email notice, as well as in PLC logic/compiler.
If all you want is rename the web GUI, for WC32, you can get GUI source and modify it yourself, and regenerate the web GUI. But that will not change the email notification and PLC logic. WC8 has no easy way for user to modify the web GUI.