How to modify Dockerfile?

Yup, I see that, but each time I rebuild I get copy errors:

## Any custom commands to run after building
run:
  - exec: echo "Beginning of custom commands"
  ## If you want to set the 'From' email address for your first registration, uncomment and change:
  ## After getting the first signup email, re-comment the line. It only needs to run once.
  #- exec: rails r "SiteSetting.notification_email='info@unconfigured.discourse.org'"
  
  - exec: cp /shared/rr/run_badges.sh /etc/cron.d/.
  - exec: cp /shared/rr/badges /etc/cron.d/.
  - exec: echo "End of custom commands"