Hello hubijo,
Now I understand what you wish to do -- change the Master/Slave bit under control of the running DSP program (graphical signal flow). This would allow a self-booting ADAU1701 to select Master or Slave I2S operation according to logic in your signal flow. Unfortunately, SigmaStudio includes no such function block to enable this. In addition, I cannot find in the -1701's data sheet as well as in this forum, a way for the -1701's core to modify its own control registers at runtime. Thus you'll need to include a small microcontroller in your system to access these registers via I2C or SPI,.
Best regards,
Bob