You've pretty much got it, especially the 2nd paragraph. And your right they would need a developer, or at least some familiarity with the inner workings of the

You've pretty much got it, especially the 2nd paragraph. And your right they would need a developer, or at least some familiarity with the inner workings of their own site in order to insert the code needed to award an achievement to a user. They can also manually assign achievements to users, or generate achievement claiming codes and send those out to users as they see fit.