Presumbly, because this automation only applies to future record updates its current trigger is “when record created” or “when record updated”, yes?
What you could do is duplicate the automation but set the trigger to be based on a field you can control, e.g. a checkbox. So, something like:
When checkbox is checked, run the script
This would give you the ability to pick specific records to pass through the automation. Does this work in your scenario?