Hello Ria_R, You can expand the lun, and it will not affect any current data, since the new space is already seen by the pool. The steps you posted are the correct steps to use.
Hi [NAME], we are going to purchase new drives for our unity in order to increase blocks/LUNs size. is this procedure correct ? 1. physically installing new drives. 2. expand the pool size 3  in block menu, selection each LUN then clicking on modify and increase size in "size" line it doesnt affect the current data? Thanks in advance
increase LUN size in unity 300