giving it some thought, no, you don’t need to loop at all, or use add_row() or update_row()
Quick example, not precise or including everything.
// this gets the repeater an all rows in an array
$repeater = get_field('repeater_field');
// create a new row, should be same format as returned by above
$new_row = array();
// push the new row onto the beginning of the repeater
array_unshift($repeater, $new_row);
// you can use update field to update the entire repeater at once
update_field('repeater_field', $repeater);