First part as in title and how to detect different webforms?
Ex. function name - hook_webform_submission_actions
Replace 'webform' with form id?
If you just want to customize the target email, webform do this quite easily.
node/123/webform/emails (where 123 is you nid) and there you can configure the recipients.
The option "component value" allows you for example to set the email regarding a select list. Configure a select list for the subject, put these values in the option textarea:
firstname.lastname@example.org|General inquiries email@example.com|Marketing
Then when the user will use webform the email will be sent to the direction chosen in the subject list.