Is it possible to reuse an alias more than once in MySQL query?
Assume there is some query which produces the output:

SELECT {expression1} AS `Qty`,
       {expression2} AS `Option`,
       {expression3} AS `Make`,
       {expression4} AS `Model`
FROM {tableset}
WHERE {conditions}


For to obtain the result which you need you must simply usethis query as a subquery:

SELECT `Qty`, `Option`, `Make`, `Model`,
       CONCAT ( CASE WHEN `Qty` &gt; 1 
                     THEN CONCAT(`Qty`, 'x ')
                     ELSE ''
                     END,
                `Option`,
                ' / ',
                `Make`,
                CASE WHEN COALESCE(`Model`, '') != ''
                     THEN CONCAT(' ', `Model`)
                     ELSE ''
                     END ) AS `Ref`
FROM ( SELECT {expression1} AS `Qty`,
              {expression2} AS `Option`,
              {expression3} AS `Make`,
              {expression4} AS `Model`
       FROM {tableset}
       WHERE {conditions} ) AS subquery


fiddle