$re = '/(?m)\s*\'\s*(.*?)\s*\'\s*(?:,\s*|$)/m';
$str = '\'MLS Number\\n2201211\\nCounty\\nCass\\nCity\\nRaymore\\nSub Div\\nEvan Brook\\nType\\nSingle Family\\nFloor Plan Description\\nSplit Entry\\nBdrms\\n4\\nBaths Full\\n3\\nBaths Half\\n0\\nAge Description\\n16-20 Years\\nYear Built\\n2003\\nSqft Main\\n1500\\nSQFT MAIN SOURCE\\nOwner\\nBelow Grade Finished Sq Ft\\n500\\nBelow Grade Finished Sq Ft Source\\nOwner\\nSqft\\n2000\\nLot Size\\n115x130\\nSchool District\\nRaymore-Peculiar\\nLegal Description\\nEVAN-BROOK LOT 184\\nS Terms\\nConventional\',
\'Fireplace?\\nY\\nFireplace Description\\nFamily Room\\nBasement\\nY\\nBasement Description\\nConcrete, Finished, Walk Out\\nDining Area Description\\nKit/Dining Combo\\nUtility Room\\nOff The Kitchen, Laundry Room\\nOther Room\\nFamily Room\\nInterior Features\\nKitchen Island, Painted Cabinets, Vaulted Ceiling, Walk-In Closet, Whirlpool Tub, Wood Floor\\nEquipment\\nCeiling Fan(s), Dishwasher, Disposal, Gar Door Opener(s), Rng/Oven- Electric, Refrigerator, Stainless Appliances\',
\'Rooms\\nLiving Room\\nLevel 1\\nKitchen\\nLevel 1\\nLiving Rm- 2nd\\nLevel B\\nBathroom Full\\nLevel 1\\nMaster Bedroom\\nLevel 1\\nMaster Bathroom\\nLevel 1\\nSecond Bedroom\\nLevel 1\\nThird Bedroom\\nLevel 1\\nFourth Bedroom\\nLevel B\\n2nd Full Bath\\nLevel B\',
\'Garage/Parking?\\nY\\nGarage/Parking #\\n3\\nGarage Description\\nAttached, Side Entry\\nConstruction\\nFrame\\nArchitecture\\nTraditional\\nRoof\\nComposition\\nLot Description\\nCorner Lot\\nIn Floodplain\\nNo\\nExterior Features\\nDeck, Fence- Wood, Porch, Storage Shed\',
\'Central Air\\nY\\nHeat\\nForced Air Gas\\nCool\\nCentral Electric\\nWater\\nCity/Public\\nSewer\\nCity/Public\'
';
$subst = "\1\\n";
$result = preg_replace($re, $subst, $str);
echo "The result of the substitution is ".$result;
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php