The licences would need converting so for example you will finish with a JAR CPL or EASA CPL. You would need to convert this and your IR and anyother ratings to FAA standards.
You would need ot pass a FAA medical and also i believe sit FAA ATPL exams.
Im a little surprised that someone studying to become a commercial pilot has never heard of the difference between FAA and JAR/EASA.
Good luck!