It's nice to see you here in the QuickBooks Community, @accounts540.
The option to modify the Remittance Advice template form is unavailable and works as designed in the current offerings. What we can do for now is manually edit the message upon sending the remittance.
While this option is unavailable, I recommend sending your feedback to our Product Development Team so they can review it and consider implementing it in future updates. Here's how:
Go to the Gear icon at the top.
Type in your feedback and product suggestions.
Click Next to submit them.
Need more help with performing any supplier-related activities? Our self-help articles contain topics about managing your money-out transactions, processing purchase orders, and recording expenses or bills, to name a few.
Feel free to comment below if you have questions other than customising remittance advice. I'm here to answer it for you. Take care.