Hi,
you can do that with many methods, that depends on what you want to manage.
On Customer card
Using "Lot Size" Production on customer card (quantity multiplier)
Changing BOM to item before launching MRP/MPS (BOM defined with quantity multiplier)
Using fixed reorderind policy with fiexd reorder quantity or using order multiple
On Calculate Plan
Using Production Forecast quantity for period
On requistion worksheet
Using recurring requistion worksheet with forecast
On Production Order
Changing Qty on Production Order Line
Changing BOM on Producton Order Component using multiplier, byself item consuming (if you need calculate MRP with quantity multiplier)