I suggest that you add a placeholder person to your tree with a “Gramps” surname. Then add a Note detailing the manual patch and a link to this discussion. And link the awk script as media or (more rot resistantly) paste the script into a Note. You can use a custom Type for the note… like Patch or Hack. Use the Private switch for the placeholder person.
Anytime the report is updated, your patch will revert. So having a workflow documented is helpful.
Have you noticed this Discouse thread:
I hoped that it would become another place where users could share their customizations for Gramps. (So they could recollect what needing tweaking after the next update. )