Rewriting mail headers

[Archeopteryx]

Hello everybody,
I'm currently developing an automated spam complainer which is still in
its infancy.

The program parses the mail message and makes some checks trying to
identify the origin of the message among the fake header lines.

For diagnostic purposes I need to rewrite the subject field of the parsed
message adding some characters.

Is there a way (I'm using the email package) to do this with some python
module?

Thanks in advance

A.