Agreed, as a person who administrate what will be 5 instances it is very difficult to understand which instance is which both in login and in emails coming from the system.
That is the way to do it but I would, if possible, see if you can encrypt/decrypt the string and not pass emails in the URL as plain text - otherwise your database could be open fo...
You may have to anagrammatically work this out using a field to hold a data value change - as it will need to be a trigger. Be wary of too many webhook calls though as they can slo...
You will can get them via List ID, Program ID or via Filter. For larger batches you will have to iterate though them grabbing batches of 300 at a time.