March 12 - Standard & Poor's Ratings Services said today that the March 9, 2012, Federal Energy Regulatory Commission's (FERC) approval of the merger of Exelon Corp. (BBB/Stable/A-2) and Constellation Energy Group Inc. (BBB-/Watch Pos/A-3) would not immediately affect ratings. We expected the FERC approval following approvals from the Maryland Public Service Commission and the PJM Interconnection market monitor, but also note the record-setting fine the FERC levied on Constellation for alleged