Package configurations taking priority over environment variables

[Enet4]

I have a use case where I would like environment variable definitions to override properties to envify, the default values of which would be contained in the package.json file. Something like this:

  "scripts" {
    "build-yes": "MY_VAR=YES browserify .",
    "build": "browserify ."
  },
  "browserify": {
    "transform": [
      "babelify",
      "browserify-shim",
      [
        "envify",
        {
          "MY_VAR": "NO"
        }
      ]
    ]
  }

Unfortunately, the re-definition derived from the script "build-yes" does not take place. Removing the definition of "MY_VAR":"NO" in the package is the only way for "MY_VAR=YES" to reach the transform. Is this the desired behaviour? Could these priorities be reconsidered?