Customizing the Subject Line for Automated Emails

Hello Everyone,

Any ideas on how to change the subject line for automated emails sent via transaction. 

For example, we Create a Credit Memo, check the "To Be Emailed" checkbox and it will send an email to our customer.  The problem is that we use a totally different # to reference the Credit rather than the NS document #. 

To avoid confusion and especially to avoid customers taking the same credit twice because of the double #'s, we have removed all the transaction numbers other than the one that we use from the printed and emailed version of the transaction.  The only problem is that the Subject Title as well as the attachment (if you turn send HTML email off) both has the NS document # there.  Is there a way to remove that and replace it with our own #?