A system for securely updating an electronic transaction card held by an account holder with an additional account and/or account data is described. A dynamic transaction card may be securely updated with an additional account by using pre-stored shell data and/or inactive data, whereby the pre-stored shell data may be populated using data received from an issuer system and/or the inactive data may be activated via an activation signal received from a mobile device. A backend server may determine, via a fraud determination, expiration determination, and/or user-request, that new account data should be transmitted to an account holder. The dynamic transaction card may receive the data associated with a notification, update a display, instruct an EMV applet to use a key associated with a received EMV key identifier for signatures, and/or update any additional data stored on the dynamic transaction card.