To create a custom transaction code for a Report Painter report:
1. Use transaction SE93 to create a parameter transaction with a descriptive name and select 'Skip Initial Screen'.
2. Map the transaction to the necessary objects like S_Program using transaction SU24.
3. Add required values like the report type, name, and library to ensure users can run the report without errors from a security perspective.
4. Transport the transaction code to production for end users via the standard SAP transport process.