I appreciate you for joining this thread, @EhudG.

Let me provide some information here about customizing sales forms in QuickBooks Online.

Out of the three customization types available, you can only make unique changes to each template when you modify details on the Design option. That means changing the content, and the email section will automatically update everything. The one you’ve experienced is how the program works. 

Having different email subject lines or messages to a recurring template is a great idea. However, it's unavailable at the moment. If you have a specific message to your customer, consider using the Message on invoice field of the recurring transaction.   

Here’s how:

1. Go to the Gear icon and select Recurring Transactions.
2. Click Edit on your recurring template.
3. Enter the details on the Message on invoice box.
4. Save template.
   

To help you out in personalising and handling recurring transactions, you can check out these articles: 

• Review your recurring transactions in QuickBooks Online
• Import custom form styles for invoices or estimates

Drop a comment below if you have any other template concerns. We’ll be happy to help you out.