Solution : https://service.sap.com/sap/support/notes/106527 (SAP Service marketplace login required)
Key words : 
additional key words ale, distribute material master data, customized material master, maintain customer-specific, customer-specific data, assigning data directly, enhance table marm, unit-dependent fields, customer-specific fields, marm structure directly
Related Notes : 
       
| 553264 | MM01: Reference handling for user-defined MARM/MAKT fields | 
| 107721 | User-specific enhancement of table MAKT | 
| 44410 | Integrating cust.-specific fields in matl master |