The Messaging Workflow is changed when the Multiple Event Registration add-on is active… If a registration approved message is generated and it contains information on multiple registrations across multiple events, then the global template for registration approved messages is used instead of Custom Messages
In our case, we need each Custom Message Template for Registration Approved to be sent. ie. a separate email to be sent for each event registered using Multi Event Registration.
Is there a way to roll-back this particular improvement on our website?
I checked into this and currently, it is not possible to change the message system to use a custom message when using the Multi Event Registration add-on and registrations are spread across multiple events due to the way data is pulled in for the messages.
There is no way to workaround the current set up, unfortunately.