Edit the Subject in Outlook Email Messages

I use Outlook 2010 and 2013 mostly, where I used the Other Actions button "Edit message" command to annotate messages I have received. (For example, to change a subject like "A question for you" to something more specific, to more easily find it again.)
In Outlook 2016, I can still use the "Edit message" command, but it no longer lets me change the Subject, only the message body. Is this ability gone, or have I overlooked something?

Outlook 2016 (and Outlook 2013) have a compact header option which reduces the amount of space it wastes on smaller screens and the default is on compact.

The compact header doesn’t support editing the subject field. Fortunately, all you need to do is expand the header to get it into its Edit mode. (This setting is persistent – it will stay expanded until you click the caret again.)

To expand and collapse the header, click the caret on the lower right part of header area. After it's expanded, click in the subject field and begin typing. You can select text to type over it or backspace to delete it.

When you use Conversation view, you'll see the original subject in the Conversation group name. The edited subject will display in the reading pane or opened message.

You don’t need to go into Edit mode to edit the subject in any version of Outlook. Just open a message begin typing in the subject field. You will need to open the message – the Subject field in not editable in the Reading Pane.