This screencast shows what happens if you make changes to configuration normally controlled by a feature. It also shows how you can revert these changes, and go back to the configuration defined by the feature. In short:
- In default mode (most) settings are read from the feature module code, and there are no database entries for things like Views and field configuration.
- When you change the configuration, there are entries written to the database describing the new configuration.
- When there is configuration in the database, Drupal will prefer that over anything defined in code. Thus, your configuration changes will have effect on how the site works, while there is different configuration left in the feature module code.
- Any feature with altered configuration will be noted as overridden in the list of features. If you have the Diff module installed, you can view exactly what these changes are.
- You can revert (groups of) components to the state defined by the feature. This (normally) wipes the database of the entries defining the overrides, and so Drupal reads from the code again.
(As a side point: Some exportables cannot be read from code, such as the variables exported by Strongarm. When reverting these, the corresponding database entries are updated rather than wiped. Settings like these are sometimes refered to as faux exportables.)