If you desire to increase the sensor sampling rate in the V5.00 library from 200Hz to 400Hz, a change is required to the FXOS8700_Init() function in drivers.h.
You will need to modify the 2nd write to FXOS8700_CTRL_REG1 from a value of 0x0D to 0x05. The changes the output data rate as per Table 33 in the data sheet.
The FXAS2100X_ReadData function (used to initialize the FXAS21002 gyroscope) DOES have the code necessary to bump the rate to 400Hz once you change
the value of SENSORFS to 400 at the bottom of build.h.
An important caveat is to not exceed the MIPS rating of whichever MCU you are using. Cortex-M4F devices will obviously be able to run at higher sampling/fusion rates than those based on Cortex-M0+. To test this post, I successfully ran at 400Hz sampling / 100Hz fusion rate using the V5.00 library.