The manual states that you can modify the file but nothing about adding new fields.
Yes, it's possible to add new fields as well.
You'll need to map CCM profile field with External Field for AD or SharePoint profile. In the CCM configuration xml file (it's either \TEMPLATE\XML\CCMProfilesADSyncConfig.xml
or \TEMPLATE\XML\CCMProfilesSPSyncConfig.xml) you'll need to specify:
- common name for AD attribute that you have created (e.g. how to create a custom AD attribute)
- property name for SharePoint profile that you have created.