https://userapps.support.sap.com/sap/support/knowledge/en/3039414
3039414 - SAP RU-FI: BAdI for Tax Agent Operations J_3RF_TAX_AGENT_OPERATIONS | SAP Knowledge Base...
You would like to change some data in selected document chain that are processed by transaction J3RF_TAXAGENT_OPERAT / program J_3RF_TAX_AGENT_OPERATIONS...