I did this 2002 when I moved from Germany tot he US. First it was great because they moved also the credit history to my new US ss-number. I called the us card service exchanged my gold Germany card for a us gold card (was a member for 3 years @ that time) Additional I wanted to et a real credit card so my credit report locks better. In Germany i had a blue card for private charges so I wanted to move that card as well. That move was not so easy because in the us that is a card with a real credit line. After talking to 2-3 supervisors they moved it with a 5000 USD credit line. For Amex membership rewards the move was easy the just moved it with the gold card. exchange rate was 1:1 no questions asked....
Juergen