I've been advocating the ability to "split conversation" for some time
now. This would allow you to do what you suggest. The "conversations"
feature of gmail is both limited andlimiting. I'd also like to rename
the topics of OTHER people's email sent to me. That way I can group it
into a conversation if I want, or change the name according to my
preferences for organization (some of my co-workers are a bit lazy
with the titles of their emails). By being able to split and combine
conversations, you could print one, rename one, remove one, put
separate labels on separate emails WITHIN one conversation (right now
I have stars on different emails in a conversation, but only so many
stars mean so many things). Split conversation would allow you to also
mark ONE email within a convo as "mark us unread" instead of it always
making very email in that conversation unread.
Star me, so people will read this!
Jacob606