You can create/save as many customized invoice templates you want out of available five form styles.
To do this:
Company Gear (upper right corner) > settings > custom form styles > choose form style > go to drop-down arrow next to SAVE blue button (do not just save it) > choose save as (name your template) > select form type (like invoice, sales receipt or estimate) > DONE
CAUTION: They missed DELETE button. Or even “Edit” button to change to different form style. Hope update coming soon!!!