PROP NICK
The NICK property is a property that contains either the nickname of the client, or an "extended" display name, that may contain things like spaces, or other characters not allowed by RFC1459 or the IRCX extensions. Clients that support this field, should use whatever the "NICK" property specifies when displaying messages from users.
Privilege: User
Attribute: Read/Write (Write via the /nick command)
Examples:
/prop steve nick Steven J. Smith