Is it possible to change the subject of the original mail with php before reaching the inbox?

Is it possible to change the subject of the original mail with php before
reaching the inbox?

i am currently reading the mails from mailserver and i would like to
change the subject of the all the mail in the mailserver with appending
some character to it and send it to user inbox.
is it possible to do with php, if it so how can i do it?
<?php
require_once('MimeMailParser.class.php');
$path = 'path/to/mail.txt';
$Parser = new MimeMailParser();
$Parser->setPath($path);
$to = $Parser->getHeader('to');
$from = $Parser->getHeader('from');
$subject = $Parser->getHeader('subject');
$text = $Parser->getMessageBody('text');
$html = $Parser->getMessageBody('html');
$attachments = $Parser->getAttachments();
?>