npm edit <pkg>[/<subpkg>...]
Selects a (sub)dependency in the current working directory and opens the package folder in the default editor (or whatever you've configured as the npm editor config -- see npm-config npm-config).
After it has been edited, the package is rebuilt so as to pick up any changes in compiled packages.
For instance, you can do npm install connect to install connect into your package, and then npm edit connect to make a few changes to your locally installed copy.
The command to run for npm edit or npm config edit.