Add new item type and replace column title

// add new item type (working)

function add_sizeproduct_line_item_type( $types = array() ) {
	$types = array_merge( $types, array( 'sizeproduct' => si__( 'Size Product' ) ) );
	return $types;
}
add_filter( 'si_line_item_types',  'add_sizeproduct_line_item_type' );


// replace new item types column 'rate' with 'Per SQM' (not working)

function add_persqm( $columns = array(), $type = 'sizeproduct' )  {
        $replace = array( 1 => "Per SQM");
	return $replace;
}
add_filter( 'si_line_item_columns', 'add_persqm' );