Modifying existing DB records

[treygriffith]

In #149, the question came up as to how to modify existing database records through a pull request. It can happen (although hopefully not too frequently) that existing records need to be modified for a new feature, or just a refactor of an existing feature, to work properly.

I've never done a database migration with Mongo before, but a tool like mongo-migrate might be good for this. Does anyone have thoughts on the best way to handle cases like this?