Special Orders No. 254 of 25 Oct 1864 (shown on pp. 1170 & 1171 of O.R. Series 1 - Volume 42, Part III) is what you're looking for. This ammended Special Orders No. 161 of 11 Jul 1864 (shown on pp. 763 & 764 of O.R. Series 1 - Volume 40, Part III) to transfer the Seventh Georgia Cavalry (instead of Phillips' Legion Cavalry) to Gary's Brigade and Phillips' Legion Cavalry (instead of the Seventh Georgia Cavalry) to Young's Brigade.