Hello,
The blhost baudrate can be changed with the -p/--port<name>[<speed>] option. For example, >blhost.exe -p COM1,57600 -- get-property 1.
If you are referring to the baud rate of your MCU running the bootloader, for the UART peripheral, the baudrate is automatically determined with the first ping command received from the blhost.
For more information on the blhost tool, please refer to the "C:\NXP\NXP_Kinetis_Bootloader_2_0_0\doc\Kinetis blhost User's Guide.pdf" document included in the KBOOT package.
Regards,
Gerardo