Are you trying to do something like this?
WITH CTE_SalesSeparated AS (
SELECT s.[Date], s.[Country], s.[Year],
coalesce(ld.[Brand] + ' ' + which, s.Brand) as Brand,
s.SalesCount * coalesce(ld.factor, 1) as SalesCOunt
FROM CTE_Sales s LEFT JOIN
(SELECT 'HP' as Brand, 'LapTop' as which, 0.8 as factor UNION ALL
SELECT 'HP' as Brand, 'DeskTop' as which, 0.2 as factor
) ld
ON s.Brand = ld.Brand
)