B737 Captain reported he mistakenly notified Dispatch prior to pushback that the Dangerous Goods were onboard instead of following the new company procedure of sending the company code. Captain realized his error and sent the company code prior to taxi.

Narrative

During cockpit setup ACARS sent the preliminary dangerous goods notification to the printer. I reviewed the bulletin on the new requirement to acknowledge receipt of the final dangerous goods manifest prior to brake release on pushback. I even briefed this during our preflight brief as a threat and had the MISC ACARS report screen up on the CDU to do so at the proper time. I knew that the code was Company Code as well but this was to be the first time I had to acknowledge the receipt of dangerous goods since this new procedure came into effect.Just prior to push things got a little hectic for me. We had just come off minimum rest for a late arrival the night before. We had a jump seater to deal with. The gate agent gave me the wrong form and had to get the correct pilot reconciliation form from her after she left the flight deck and we had a passenger duplicate seat that had to be worked out with eventually deplaning two passengers and customer service deciding to leave their bags on board with the passengers asking to have their bags taken off the plane. After that was sorted out the dangerous goods final came out late almost at the same time as we were ready for push. So I asked for the before push checklist at the proper time; sent the dangerous goods acknowledgment. ACARS responded back and the printer started printing the dangerous goods manifest so I released brakes and pushed back thinking this was how this new procedure went. During pushback we received a warning message over ACARS to acknowledge receipt of dangerous goods. Then I realized my error; I had been using DG as the code to acknowledge receipt and not Company Code. So before taxiing I sent the correct Company Code and got the proper acknowledgment back from ACARS and we proceeded outbound.