Although I have not tried it by myself, following strategy might work
(1) Set the SCB module has "Clock from terminal"
(2) Connect clock to the SCB module
(3) Configure the Clock for fractional divider
check "Use fractional divider"
(4) Then an API called Clock_SetFractionalDividerRegister will be available.
In my sample the name will be "Clock_12MHz_SetFractionalDividerRegister",
and I'm not sure if "UART" was right sample for this kind of test...