Package configurations taking priority over environment variables

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:

``` json
"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?