A weird edge case came up today around a buildpack that turned out to be unneeded for my application. How do you change the Buildpack once you’ve associated it with your application? It turns out that a Buildpack is essentially just a piece of config, so you can see it and change it by using the heroku config command and the config variable name BUILDPACK_URL.
In my case I just needed to remove the configured Buildpack with a simple heroku config unset command:
heroku config:unset BUILDPACK_URL