Mail-Changing Subject header text

[John Erdman]

Before OS10.2.6, I used Eudora as my email client.

With Eudora I could change the title of incoming mail when I wanted to 
save it.   I found it useful to be able to retitle the Subject to 
better describe the content I was interested in as many titles do not 
reflect the content.

Anyhow... now that I've converted to OSX I use the included mail app 
exclusively. I generally like it better than Eudora, but I find I can't 
change the titles on mail I've saved in a mailbox. Is there a way to do 
that?

Thanks,
John