Hi Eva,
To populate additional field automatically in APO via CIF, you can use the outbound userexit (CIFMAT01) in ECC or inbound userexit (EXIT_/SAPAPO/SAPLCIF_PROD_001) on the APO side.
If the "merchandise category" field is available in ECC in master data fields or in some other table, then you can implement the outbound userexit in ECC (CIFMAT01) and populate the additional attributes in the product master .
SAP note "1534157 - Transfer of material master data from R/3 to APO : Extend CIF structure via User Exit" details how this can be done.
Regards,
Mitesh