This information is specific to Active Directory. MSDN has documentation for each schema attribute — e.g. CN — which documents if the attribute is “system only” or not.

For an automated process, search at the base cn=schema,cn=configuration,dc=example,dc=com with the filter (&(ldapDisplayName=AttributeName))and return the value of systemOnly. E.G. this shows that operatingSystemServicePack is user writable.

***Searching...
ldap_search_s(ld, "cn=schema,cn=configuration,dc=example,dc=com", 2, "(&(ldapDisplayName=operatingSystemServicePack))", attrList,  0, &msg)
Getting 1 entries:
Dn: CN=Operating-System-Service-Pack,CN=Schema,CN=Configuration,dc=example,dc=com
systemOnly: FALSE; 

You can also list all of the system-only attributes by using the filter (&(systemOnly=TRUE)) and returning ldapDisplayName

***Searching...
ldap_search_s(ld, "cn=schema,cn=configuration,dc=example,dc=com", 2, "(&(systemOnly=TRUE))", attrList,  0, &msg)
Getting 189 entries:
Dn: CN=OM-Object-Class,CN=Schema,CN=Configuration,dc=example,dc=com
lDAPDisplayName: oMObjectClass; 

Dn: CN=Canonical-Name,CN=Schema,CN=Configuration,dc=example,dc=com
lDAPDisplayName: canonicalName; 

Dn: CN=Managed-Objects,CN=Schema,CN=Configuration,dc=example,dc=com
lDAPDisplayName: managedObjects; 

Dn: CN=MAPI-ID,CN=Schema,CN=Configuration,dc=example,dc=com
lDAPDisplayName: mAPIID; 

Dn: CN=Mastered-By,CN=Schema,CN=Configuration,dc=example,dc=com
lDAPDisplayName: masteredBy; 

Dn: CN=Top,CN=Schema,CN=Configuration,dc=example,dc=com
lDAPDisplayName: top; 

Dn: CN=NTDS-DSA-RO,CN=Schema,CN=Configuration,dc=example,dc=com
lDAPDisplayName: nTDSDSARO; 

Dn: CN=Application-Process,CN=Schema,CN=Configuration,dc=example,dc=com
lDAPDisplayName: applicationProcess; 
...