I did some work for a client a while ago where we created a lot of email steps in Microsoft Dynamics GP workflow after which the client decided they would be using email after all and needed email on those steps activating and a custom message assigned. Rather than going through each step manually and switching the email on, I created a small script to do the job for us.
The script was for a PM Batch Approval type so also enables the include Document Attachment option.
The highlighted section is the name of the E-Mail Message ID to assign:
UPDATE
WF100003
SET
EmailMessageID = 'AZRCRV PO APPROVAL'
,Workflow_Step_Send_Email = 1
,WFIncludeDocumentAttach = 1
WHERE
Workflow_Step_Send_Email = 0
As always before running a script make sure you understand what it does, test it on a test system before deploying live and make sure you have a good backup before running and verify afterwards.