Solution : https://service.sap.com/sap/support/notes/325546 (SAP Service marketplace login required)
Summary : 
      This SAP Note details how to introduce user-defined fields in CO line item reports through customer exits, specifically in actual, planned, commitment, and budget reports. It involves utilizing Transaction SMOD/CMOD for accessing the required customer exits and project "COOMEP01" for documentation. Key activities include extending report output structures, programming the appropriate exits, and maintaining view V_TKALV to ensure the new fields display correctly. Extensive knowledge in ABAP programming and familiarity with transactions SMOD and CMOD are prerequisites. The example provided covers extending actual cost reports with a specific "Cost Center Manager" field.
Key words : 
output structure   customer include structure  actual      kaep_coac          ci_rkpos  plan        kaep_copl          ci_kaep_copl  commitment  kaep_cm            ci_rkpoa  budget      kaep_bdg          ci_kaep_bdgthus, actual      exit_saplkaep_001      plan        exit_saplkaep_002      commitment  exit_saplkaep_003      budget      exit_saplkaep_004the exits, output structures include customer include structures, read       zzverak      kokrs       zzverak      objnr       zzverak       budat, data element/component type enter verak, actual costs line item reports, actual cost line item report, planned costs line item reports, budget line item reports, commitment line item report
Related Notes : 
       
| 896531 | CO-EP reports: Customer-specific authorization checks | 
| 668514 | FAQ 2: Line item reports | 
| 591963 | Co EP-reports: Restriction on characteristic BELKZ | 
| 562169 | CO line item reports: WBS elements not displayed completely | 
| 546414 | CO-EP reports: Commitment at funds & functions' | 
| 359691 | CO line item reports: Missing fields | 
| 331416 | CO line item reports: EXIT_SAPLKAEP_009 | 
| 327821 | CO line item reports: fields are not filled | 
| 324628 | CO-EP rep.:Too much data/dump w/call via rep/rep interf. | 
| 122975 | Resetting buffering of ALV field catalog |