Hello Abhishek,
As per standard SAP this mayn't be possible if both alternate BOM's are having same validity
If the alternate BOM's are having two different validity dates then you can specify the BOM based on the validity
Or
Read PP Master data based on BOM Validity
or
Through WORKORDER_UPDATE BADI you can show a popup to the user to select the BOM based on validity
Regards,
Venkatesh..