I too have this same problem! I am a scheduler for a high level government agency head. Her calendar receives many invites from outside our agency and I ALWAYS have been able to add talking points, agenda's, background to the invite and even make changes to the subject line noting attachments which can only be seen by her. I don't know who thought it was a good idea to change a very helpful feature in Outlook and I know I'm not the only one who is now facing having to do things differently. PLEASE PUT BACK THIS FEATURE ASAP!!!
When you decide there's something you want to change in Outlook, maybe ask people who use Outlook 24/7 what they think before making any changes.
Frustrated Scheduler
Carol