If the Quantity of the original item is updated, from one to two, the system will offer to update the quantities of the associated items, and will do so in the default quantities, this can be amended after if necessary.
If you choose Yes then any associated items on the sales order will be adjusted. For each one of the original item, the quantities will be adjusted accordingly.
NB: The quantities will be adjusted based on the ratio you applied when you first added the associated lines, so something to bear in mind when you adjust the quantities.
If the Quantity is later reduced, the system will again check and offer to reduce the quantity of the associated items by the multiplier added.
Just like the adjust message when you were adding to your quantities the same message will pop up when you planning to reduce your orginal item.