Solution : https://service.sap.com/sap/support/notes/1052648 (SAP Service marketplace login required)
Summary : 
      This SAP Note guides users on migrating or converting existing transfer and update rules into transformations within the Data Warehousing Workbench (transaction RSA1). The note highlights limitations in the migration tool, which may not handle complex scenarios effectively, potentially resulting in incomplete or incorrect transformations. Users are advised to make manual adjustments post-migration for complex routines. Issues, restrictions, and the requirement for manual adjustments are detailed within the note. Additionally, related notes that address known migration errors are listed, with a recommendation to implement these if issues arise. Corrections in transformations need a re-migration or manual adjustments if the transformation contains errors.
Key words : 
'<--- insert'    sourcesystem  type rsslogsys          '<--- insert'  changing    result        type _ty_s_tg_1_full-<target_fieldname>    returncode, l_sourcesystem                      '<--- insert'      source_fields-record      tran_structure    changing      result      l_subrcform compute_<target_fieldname>, source_fields-record      tran_structure    changing      result      l_subrc, comm_structure  changing    result    l_subrc    l_abort, migrated update rule call  perform routine_'m', section 'related notes' lists notes, sy-subrc  raising    cx_sy_arithmetic_error    cx_sy_conversion_error, source code area '2nd part global', rule-specific type _ty_s_sc_1__rule_'n', tran_structure  type _ty_s_sc_1__rule_'n'
Related Notes : 
       
| 1554150 | NW BW 7.0 (Support Package 26): Dump during migration | 
| 1527023 | Technical enhancement: Routine source code; direct migration | 
| 1369395 | Transformations generated from migration: Repair tools | 
| 1364916 | Migration generates formula with incorrect 'FORMTP' | 
| 1351125 | ASSERTION_FAILED in class CL_RSTRAN_GEN_STEP->SET_CONTAINER | 
| 1345161 | Migration transfer rule/update rule: Syntax error | 
| 1325124 | Migration: Syntax error in start routine | 
| 1292311 | Extraction monitor probs. for transformations from migration | 
| 1260582 | Transformations for Product corrupted in BI Content | 
| 1244935 | Endless loop in CL_FOBU_FORMULA->ALL_OPERANDS_GET_INTERNAL | 
| 1236154 | 2LIS_13_VDITM Transformation internal error: 38 0CRM_PROD | 
| 1235825 | Error BRAIN 381 occurs for currency translation | 
| 1227667 | Guidelines for expert routine: Design rules | 
| 1171547 | Incomplete migration of routines to transformation | 
| 1116410 | BI7.0(SP17) Dump when editing transformations | 
| 1115010 | BI7.0(SP17): Migration of update rule incorrect | 
| 1080640 | Migration of rule type 'Read master data' 70SP16/71SPS04 | 
| 1077930 | Transformation with template: Errors RSTRAN523 and RSTRAN669 | 
| 1076291 | RECORD_NO and RECORD_ALL not filled | 
| 1071255 | Short dump during migration after transformation | 
| 1069325 | Problems occur when you create a constant rule | 
| 1052644 | Tranformation with template (migration); RSTRAN669 in log | 
| 1048423 | R7 105 during migration of update rules | 
| 1046544 | Problems: Migrating w/source fields with fixed unit/currency | 
| 1045192 | Syntax error: 'RECORD field missing in SOURCE_FIELDS' | 
| 981194 | Creating transformation using template in SP09/SP10 | 
| 979607 | Runtime attribute: For example, source system is unavailable |