How is the bootloader baud rate changed on the SaBLEx?

Please see section 8.2.2.1.1 from the TI CC 2640 reference guide on this. Below is a copy of that section. 8.2.2.1 UART Transport The connections required to use the UART port are the following two pins: UART0 TX and UART0 RX. The device communicating with the bootloader drives the UART0 RX pin on the CC26xx and CC13xx, while the CC26xx and CC13xx devices drive the UART0 TX pin. While the baud rate is flexible, the UART serial format is fixed at 8 data bits, no parity, and 1 stop bit. The bootloader automatically detects the baud rate for communication. The only requirement is that the baud rate must be no more than 1/16 of the frequency of the UART module clock in CC26xx and CC13xx devices. 8.2.2.1.1 UART Baud Rate Automatic Detection The bootloader provides a method to automatically detect the UART baud rate being used to communicate with it. To synchronize with the host, the bootloader must to receive 2 bytes with the value of 0x55. If synchronization succeeds, the bootloader returns an acknowledge consisting of 2 bytes with the values of 0x00 and 0xCC. If synchronization fails, the bootloader waits for synchronization attempts. In the automatic-detection function, the UART0 RX pin is monitored for edges using GPIO interrupts. When enough edges are detected, the bootloader determines the ratio of baud rate and frequency needed to program the UART. The UART module system clock must be at least 16 times the baud rate; thus, the maximum baud rate can be no higher than 3 Mbaud (48 MHz divided by 16). The maximum baud rate is restricted to 1.6 Mbaud because of the firmware function that detects the transfer rate of the host.