Hello there, @marthinus.
Allow me to share some information about using Custom form styles in QuickBooks Online.
Currently, an option or keystroke to have a different email message for each template is unavailable. The system is designed to apply the changes to all existing forms.
I appreciate your input on this feature. We'll continue to update the features of the product, and this preference might be available in the future.
While we assess this, I recommend you visit our QuickBooks Blog to stay updated with all the changes.
For additional information, I've attached an article about how to customise your invoice emails in QuickBooks: Customise your invoice emails.
I appreciate you for taking the time to visit us here today, and I look forward to your response.
