Dear Javier H., My apologies for the delay on the answer, As you can see from these devices the only one that have the Flexio Module is the K82, what do you want to do it is possible from the MCU side, you can switch from uart to I2C at will, the problem is on the hardware since the lines for I2C are open drain it will not work properly with the lines of UART.
check the images in the HMI section the only one that have the FlexIO is the K82



Best regards.
Jonathan