They can't change how vBulletin works, and with vB, that's typically a moderator feature. Well, technically, they can change the limit, but most admins are too weary to change the limit. In fact, I've never seen an admin allow anything above 5 minutes, which is the default setting.
It's best to change the title during the 5 minutes after you submit the thread, though I understand that isn't the case with updates...
Why can't you request that a moderator update it?