Click "Reply All" AND change subject line?

I used to be able to click "Reply All" on a message and then change the subject line but this doesn't seem possible anymore. Am I missing something? That was something I would do often. I can't even copy the list of people the message was sent to and paste it in the TO box of a new message. (Or create a group out of those addresses to plug in).

Suggestions? Or do I have to save each email address to my contact list individually and then make sure I get them all in the To or CC box of a new message. Quite the pain if that is the case.