Not able to change the key value of banner_message_text in gconf-editor

Hi,

I tried to change the value of banner_message_text under /apps/gdm/simple-greeter/ using gconf-editor. But it is not allowing me to edit the value of the key and reports "The key is not writable".

OS Version: RHEL 6.5
User : root

Please find attached screen shot for the same.