CCS/MSP432P401R: Changing the clock used in "__delay_cycles();"

__delay_cycles is based on (calibrated) instruction execution, so it implicitly uses MCLK. If you set HSMCLK to the same source/divisor as MCLK, you'll be counting HSMCLKs as well, but that's a bit circular and probably not what you want.

As far as I know the only device which can use HSMCLK is the ADC14, which is cumbersome as a timing device.

If you can describe your overall goal, maybe someone can think of a different way to get there.