AN AIRBUS FLIGHT CREW RETURNED TO GATE AFTER TAKING RUNWAY DUE TO COMPANY MAINT CONTROL ISSUING CONFLICTING APPROACH CATEGORIES; CAT TWO AND CAT THREE. ON ACFT MAINT RELEASE AFTER BSCU CHANGED.

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AFTER ARRIVING AT ACFT WE DISCOVERED INBOUND LOG OF BRAKES GRABBING DURING GENERATOR #2 SHUTDOWN. MAINT CTL AND LINE MAINT DISAGREED ABOUT FIX. AFTER CHANGING BSCU WE DEPARTED THE GATE WITH AUTOBRAKES DEFERRED. WE SENT ACARS TO MAINT CTL AFTER TESTING GENERATOR #2 AS REQUESTED. AFTER TAKING RWY WE GOT ACARS TO CLARIFY OUR CAT STATUS FROM 2 SEPARATE MAINT CTLRS. AFTER RETURNING TO THE GATE WE DEPARTED WITH NEW FPF AND MAINT RELEASE. MAINT RELEASE WAS INVALIDATED BY MAINT CTL WHILE WE WERE AT RWY. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: REPORTER STATED THE CONFUSION DEVELOPED AFTER LOCAL MAINT REPLACED THE BRAKE STEERING CONTROL UNIT (BSCU) AND DOWN GRADED THE ACFT'S APPROACH CATEGORY FROM A CAT THREE TO A CATEGORY TWO. THIS WAS DONE TO EXPEDITE THE ACFT'S RELEASE; OTHERWISE THE MAINT CHECK FOR A CATEGORY THREE RATING WOULD REQUIRE A LENGTHIER DELAY BEFORE DEPARTURE. COMPANY MAINT CONTROL WANTED A CONFIRMATION OF THE ACFT'S ACTUAL APPROACH CATEGORY STATUS AND DISAGREEING WITH LOCAL MAINT ON WHAT OPS CHECK WERE; OR WERE NOT; REQUIRED TO BE ACCOMPLISHED TO MAINTAIN CATEGORY THREE STATUS.