Is there a way to import a customs invoice of products, without changing a template?

I appreciate you reaching out in the QuickBooks Community, ADMAIORA.

QuickBooks does not support importing customised invoices, as the system processes imported data according to its required format. 

Whether you use an existing spreadsheet or a QuickBooks sample template, your invoices must meet the specified requirements. To learn more about the prerequisites when importing invoices, you can check out this article: Import multiple invoices at once in QuickBooks Online.

However, if you’d like to customise your invoices, you can create a new customised invoice template directly within QBO. Once the template is set up, you can recreate the imported invoices using your newly customized template, ensuring they align with your specific requirements.

You can revisit this thread if you have follow-up questions.