Set Based way to order items with SQL

so you have a list of rules or something and you want your users to be able to change the processing order

DECLARE @new_item_priority INT = 1
DECLARE @reorder_priority AS TABLE (item_id INT, item_priority INT )

INSERT @reorder_priority 
SELECT item_id, ROW_NUMBER() OVER(ORDER BY rn) AS item_priority
FROM  (
    SELECT item_id, 
    CASE 
    WHEN item_id = @p_item_id AND @new_item_priority < item_priority THEN CAST(@new_item_priority AS FLOAT) -.1
    WHEN item_id = @p_item_id AND @new_item_priority > item_priority THEN CAST(@new_item_priority AS FLOAT) +.1
    ELSE item_priority
    END rn
    FROM dbo.items
    -- WHERE clause if needed..
) x
ORDER BY rn


UPDATE i
    SET item_priority = rp.item_priority
FROM dbo.items i
JOIN @reorder_priority rp ON rp.item_id = i.item_id