Where to add track_changes option in migrate_d2d class I have an ongoing migrate_d2d migration where I will need to be able to
detect changes on a node by node basis, and I would really like to be able to
use the functionality in the Hash source rows to detect changes feature to
do that.  However, I can't find where to add that option so that the hashes
are generated. I've tried this is my class (that overrides
DrupalNode6Migration):

$this-&gt;sourceOptions['track_changes'] = TRUE;


but the option isn't added and used. According to this referenced post on this feature, I should add it in my source constructor, but that
part is handled by migrate_d2d in the abstract DrupalMigration class. Do I
need to go down to that level to create my class just to access this
property, or is there a way I can add it from my class that overrides
Drupal6NodeMigration?
It seems you want to synchronize sites.
http://timonweb.com/using-hash-value-trackchanges-to-detect-source-data-changes-in-migrate-for-drupal-7 
If you follow on this example you have mentioned above, Filter nodes by the update time these are changed after you deployed at last. You use MigrateSourceSQL. So you able modify a query.

If you want to synchronize sites, use the module: services or feeds.