Hello Milo123,
Welcome back to the Community. QuickBooks is a flexible program that helps you streamline your work using the powerful features offered in the program. Rest assured, I'll be happy to share more info so you're on the right track.
The function to have the template edits affect just one customer isn't available in QB Desktop. Although the program is designed to apply the template edits to all customers, I can see the benefit of having this function for your business. That said, I encourage you to send feedback about this to our engineers. You can send feedback by clicking on the Help menu icon and looking for Send Feedback Online. New product ideas and improvements are based on the feedback we get from users like you.
Let me know if you have other questions by leaving a comment below. I'll be on standby.