Unconfigured SCB mode is best suited for your application and is used when you want to change the SCB modes in run-time.
I have created a sample project to demonstrate your application. The unconfigured SCB is first configured to SPI mode slave mode. RX_FIFO_NOT_EMPTY is used to receive the bytes.
To change to SPI master mode, a pin interrupt is used (application dependent). Upon button press, the SCB is configured to SPI master mode and transmits a byte of data every 500 ms to the slave.
Please let me know if it helps.