Question[s] About Blue Green Deployments

If make a new deployment via JETS_EXTRA=2 in Jets 4 for instance:

  1. In my CI/CD process, will I have to specify JETS_EXTRA=2 from this point on with every deployment i.e. JETS_ENV=production JETS_EXTRA=2 bundle exec jets deploy production
  2. If I have set, will the new deployment replace the old one automatically?