Edit subject line of email in inbox in Apple Mail In Apple Mail is there a way to edit the subject line of an email that's in the Inbox? This is just for internal filing reasons. 

Say, for example, you get sent an email with the subject line 'attn:sam'. That subject line doesn't really help me if I want to go back and find it, so could I rename that subject line somehow?
While technically it's possible, it's not trivial. You would have to write an applescript to search/replace the contents of your subject field and then use apple mail filters and run applescript based on your rule.

This is commonly done in the unix world via procmail, for example when spamassassin detects spam, procmail appends SPAM to the email subject message.

it might be better to set up rules based on subject to filter your mail into separate boxes for organization.