adding fields to 2LIS_12_VCITM datasource in ECC
There are several different ways to add fields to a logistics datasource like 2LIS_12_VCITM. If it is a pool field (a field already available in a source table) you can go to t-code LBWE and simply add it to the comm structure of the datasource. Note that before doing this you will need to drain the V3 and V2 update jobs for the datasource.

If the field you want to add is not a pool field then custom code needs to be written to append the field to the datasource or add an exit routine that populates the field when the datasource data is being transferred to BW. An exit routine is less problematic than adding an append structure for the datasource.