No. A scan of regulatory sources finds no prohibition against unilateral mass modifications. DFARS 204.70 (5) describes the contract administration office’s (in your case DCMA) implied authority to generate ARZ modifications. DCMA is not unique in issuing mass modifications; GSA uses a mass modification process to change contracts under multiple award contracts (however the process reviewed was for bilateral modifications.) The procuring contracting officer could rescind delegation of functions under FAR 42.202 (d) however the mass modification process is designed to lower the administrative burden for all parties in contracting. With an established process in place, executing administrative changes, and with delegated authority to effect such changes; the mass modification process comports with the intent and within the authority of the FAR and DFARS.