Importing JSON theme does nothing across many templates.

Hi

I have been tasked with creating a theme file that can be used to update many existing .pbix templates.

Importing the theme does not change much. I understand this is because if you modify and save any styles in Power Bi, they override the theme file styles.

How can I remove all existing styles from a .pbix template so that only my JSON theme styling is used in all the PBIX charts?

Do I have to select every individual chart and right click "Reset to Default" and select "Reset all settings to default"? Is there not a better/quicker way to reset a template styles to default across all charts?

Can't seem to find a straight answer. Thank you.