A:Answer Short answer: No, you cannot use the new sim to continue an already active line in Mint Mobile.
Long answer: Well, you can basically wait for your current term to expire, and create a new account - "Porting" your existing number to the new sim card, but it does take some finesse to get that working. I called Mint Mobile before I purchased, and I had an answer from one agent saying that is possible to continue, but when I got the card, and tried to extend my service, I had to call and find that is not supported. But you can let the current sim run out, and create a new account with number "ported" in with the new sim card.
I hope this answers your question.