Which location becomes our principal office for routing number purposes?

Several of the banks in our holding company are being merged into a single bank. The executive offices and management of the surviving bank will be housed in the former headquarters building of one of the merged banks located in one Federal Reserve territory and all the affairs of the bank will be managed out of this location including the management of the bank’s Federal Reserve account. The charter of the surviving bank will list a location in another Federal Reserve territory as the address of the bank, although the office at that location will function primarily as a branch. We currently have a routing number for each location.
Which location becomes our principal office for routing number purposes?