Changing a Multiple BOM - Special Points 
For information on options for changing multiple BOMs, see Options for Changing a Multiple BOM.
A multiple BOM groups together several alternatives. You can always only change one alternative at a time. For this reason, you must enter an alternative.
If you want to change a variant part in one alternative, choose Material BOM → Change.
If you want to change an item that is used with the same data in all alternatives (non-variable part, choose BOM group → Change.