You're already on the right track, Adam.

You can reimport a new form with amounts that include GST by using tags like <amountwithgst> instead of <amount>.

QuickBooks Online (QBO) custom templates are limited to the predefined design and settings established before import. Unlike built-in templates, which allow for toggling options like show tax inclusive amounts, imported forms pull information directly from the tags used during customization.

Let us know if you have additional questions about customizing your invoices, please don’t hesitate to revisit this thread.