Core Viewpoint - The article provides guidance on how to modify the withholding unit for special additional deductions in the personal income tax mobile app, emphasizing the necessary steps and prerequisites for taxpayers to ensure a smooth modification process [10]. Group 1: Modification Process - Taxpayers can change the withholding unit for special additional deductions by logging into the personal income tax app and navigating to the relevant sections to modify their declaration method [10]. - Before making changes, it is crucial for taxpayers to confirm that the new withholding unit is displayed in the "Employment" section of the app; if not, they should contact their current employer's tax officer [10]. Group 2: Documentation Requirements - For enterprises with branches operating across provinces, the main company is responsible for collecting and retaining documentation for R&D expense deductions, while branches can independently enjoy certain tax benefits and must keep their own records [13].