CBPO's at airports may do cargo but normally they just do passenger processing. You'd check passports and issue entry documents, interview travelers and search luggage. Usually cargo is something the more senior people do. There is no "Immigration Officer", that is what CBP Officers do, Immigration merged with Customs to form CBP.
FLETC training is different for every agency. The special agents do the same classes but CBP Officers, Border Patrol, Bureau of Prisons, Amtrack Police, Park Police etc all have different academies, they just happen to be at the same location for convienance of resources.
Depends on the position and agency.
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