Transaction or account settings submitted in the transaction request string will always override settings in the Authorize.net Merchant Interface. Most merchants rarely modify Merchant Interface settings that could impact their integration. However, changes to settings in the Merchant Interface could affect values in the transaction response, or the way information is returned in the transaction response. This could lead to unexpected behavior with the transaction response, or issues with parsing the transaction response correctly.

To avoid this, it is recommended to set fields in the transaction request string that format the transaction response on a per-transaction basis. Examples of such fields are x_test_request, x_delim_data, x_delim_char, x_encap_char, x_relay_response, x_duplicate_window, and x_response_format.

For more information, please refer to the Authorize.net Developer Center.