could you be more specific about what you want to do?
If you want to add new user attributes I recommend creating a custom aspect and behavior which will auto add a custom aspect to the new users. You would have to also override some Share code to make those custom aspect's metadata visible and editable.
Unfortunately GUID and SID are binary attributes. There is no (out of the box) mechanism you could use to sync these since you would need to translate/parse the bytes into a readable string.
Having that said, your Identity Team may want to have a reliable, non modifyable key for a user for sync but there is no such thing except these binary attributes. This means for now and for Alfresco ldap sync a user name (sAMAccountName) or group name must not change on the AD or you would get a lot of trouble ...