I think all you'd need to do is change the content of the sbsGroupListTpl chunk. If there is an existing Subscribers group with members, you'd have to change its name. Important: Don't delete it if there are existing members because the link between each user and the Subscribe Group's ID is already stored in the DB.
Here is one way to go. This would leave the group name as Subscribers, but Display Registered Vendors in the forms.
Registered Vendors==Subscribers
These would (I think) change the name of the group used:
Registered Vendors==RegisteredVendors
or
Registered Vendors==Vendors
The part after the == is will be the name of the actual User Group. I'd recommend not have any spaces in it.
None of this has been tested extensively because I've always used Subscribers.
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Notify and Subscribe work very well together. They were designed together, and in fact, when I last updated Notify most of the changes went into Subscribe. Manage Preferences should work for you as well. I use it all the time.
If you're a Subscriber at Bob's Guides (and why wouldn't you be --

), you've received regular emails from Notify. The emails contain an encrypted link to unsubscribe or Manage Your Preferences. Notify actually asks Subscribe for the link and inserts it into the email. The link points to a page that Subscribe manages.