如何安静地定制现有的MongoDB？

Supose i have a running mongodb instance(also using mongo sharding) with millions of data and thousand of transactions per second, and i have used morphia as my object-document mappe. since we want to keep project alive by bug fixing, updating and ... in some point changing the data model will be inevitable. consider below example : I have a persisted class (model) :Supose i have a running mongodb instance(also u