Can I set a customized invoice template as default?

Hi there, @wirenutskh. 

Yes, allow me to guide you through the process of making the invoice template as default in QuickBooks Online (QBO).  

Here's how:

1. Click the Gear icon, then select Custom form styles.
2. If you haven't created an invoice template yet, let's choose New style to create one.
3. However, if you have templates to choose from, select the dropdown in the Edit and then Make default.

Screenshot attached below for visual reference.  

Once set to default, it will be used for your invoices created onwards.

In addition, I've added this article as reference on how to discount invoices and sales receipts in QBO: Add a discount to an invoice or sales receipt in QuickBooks Online.

 Feel free to reply to this thread for any sales form's customizations and QBO-related questions. I'll be on the lookout. Take care.