I have three trading names under one Quickbooks account.
I have set up three separate invoice templates, and when I alter the email subject and message to customer to include the trading name for the particular business I am invoicing from, it automatically alters the same particulars in the settings of the other invoice templates.
Can this be fixed so that each template's details for sending invoices via emails, remain as I enter them?
For now, changes made in the Emails tab will be applied to all invoice templates. You'll need to change the subject and the content of the email before sending invoices.
Although, the Location tracking will let you create separate templates with different company name, address, and contact information for each business. Please see this article for more details about this feature: How To Set Up And Use Location Tracking
I will also send your feedback about the email content in your templates to our engineers. This will be tagged as a feature request and will be reviewed for future updates.