Changing the Subject line

I noticed sometimes somebody answered to a message, but added something in the subject line. I tried it, but it doesn't let me override it :( How is that done?

When you move up in status, you can change the subject line..

RANK DOES AT TIMES COME WITH THE ODD PERK.

Awww ..then I have to wait for a while. At what rank do you get to change it?

Found in the What's New section of the help section:

changed forum so only users at level of 'Junior User' or better can change the message subject [bug #145]

Thanks, I just have to hurry up that I become a "Junior" ..lol