Hello Radu,
1) IF your project is KDS+sdk without PE , please first build the KSDK lib here :
Freescale\KSDK_1.3.0\lib\ksdk_platform_lib\kds\KL27Z644
then it will generate one ksdk_platform_lib.a under "lib\ksdk_platform_lib\kds\KL27Z644\debug"
add the .a file in the compiler :

then you can use the functions under fsl_i2c_hal.h . If it still can not work , please take a screenshot about the error and sen your project to me.
and tell me you use which version of KSDK.
2) If you create project with KSDK+PE, you can directly use the I2C_HAL_SetBaudRate function .
Have a great day,
Alice Yang
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