The only way to change to order of the rows from a coding standpoint is to get the entire repeater as an array, reorganize the array and then re-save the entire repeater. the index of a row is only the order of that row in the array.
$repeater = array(
array(
// row array
'field_1' => 'value',
'field_2' => 'value'
),
array(
// row array
'field_1' => 'value',
'field_2' => 'value'
)
)
