Formatted modify and import --set-field.

[Duncaen]

Description

Fixes #488

To Do

• [x] Documentation. (If you've add a new command-line flag, for example, find the appropriate page under docs/ to describe it.)
• [x] Changelog. (Add an entry to docs/changelog.rst near the top of the document.)
• [x] Tests. (Encouraged but not strictly required.)

[sampsyo]

Awesome!! Thanks for putting this together! This looks really good at first glance; I will give it a thorough review soon.

[stale[bot]]

Is this still relevant? If so, what is blocking it? Is there anything you can do to help move it forward?

This pull request has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[sampsyo]

This is still alive.