Yes sure it can be done using /m
(MULTILINE) switch. Try this code:
$expectedData = <<<CSV
Date,Name
2013-10-09T12:11:00+01:00,SomeName
2013-10-09T12:15:00+01:00,OtherName
CSV;
$re = '/^.+$/'; // some regex here to be placed in 1st column
echo preg_replace('/^(=\d{4}-\d{2}-\d{2})[^,]+/m', $re, $expectedData);
OUTPUT:
Date,Name
/^.+$/,SomeName
/^.+$/,OtherName