Hi there, @norstar.

Allow me to share some information about the modification of the new style invoices template in QuickBooks Online (QBO).

In QuickBooks Online, any changes made to your invoices before importing them will no longer be reflected. This is because QuickBooks Online will only follow the new form style, as the old form style is no longer available.

However, if you are referring to the template, you can select or create a new template and set it as the default template for your invoice. It's important to note that the new template will not be visible on the invoice page until you print or send an invoice.

Here's how to customize the invoice form and set it as default:

1. From the Gear icon, select Custom form styles.
2. Select New style (if you haven't created one) and select Invoice.
3. Modify your template according to your preferences.
4. Then select Done.

After creating a new custom form style, you can set it as default by clicking the Edit drop-down button and then select Make default.

For your reference, you can take a look at the following write-up to help guide you with utilizing your invoice template in QuickBooks Online:  Customize invoices, estimates, and sales receipts in QuickBooks Online.

Moreover, you can check this article to learn how to receive and record invoice payments in QuickBooks Online: Record invoice payments in QuickBooks Online.

You can leave a reply if you have more questions with the invoice template features in QBO, I'll be glad to help. Keep safe!