Balanced verifies a card with the networks and issuing banks when a card is tokenized. The cards endpoint only supports a one-time POST.
There have been requests to allow a marketplace to validate the cvv2 on an existing card. The proposed use case is to request cvv2 on subsequent transactions (without asking for the card number again) to reduce risk.
Proposed interaction:
PUT on cards resource with the security_code reverifies the card
UPDATE (5/29/13): include AVS as part of the proposal.