What are the limitations when it comes to creating/editing Target Data Extension fields?

When using the Edit Target Data Extension functionality or when using the Create Data Extension functionality, the following limitations apply:

• Field Length can only be changed for field type Text.
• When creating a Data Extension, Primary Key and Nullable can be changed without limitations until the Data Extension is created. When editing a Data Extension, Primary Key and Nullable can be changed only if a field does not have Primary Key or Nullable checked.
• A Default Value cannot be set for the Email Address, Phone, and Locale fields.
• Upon editing the Target Data Extension, users can not delete fields.