Here's what you can so you'll be able to apply your customized template to the current invoice, pshc.
When you open an invoice, it will always default to the Standard template. You'll have to click Customize and select the specific template every time you open the invoice for the changes to reflect.
I've attached a screenshot for your visual guide:
For your reference, you'll want to run reports in QuickBooks Online to get the information you need.
Fill me in if you need anything else with invoices. I'll always be right here if you need further assistance.