Something like things should work:
./fah6 -forceasm -smp -verbosity 9 &
renice -n -2 -p $!
echo 0 > /sys/devices/system/cpu/cpu0/cpufreq/ondemand/ignore_nice_load
echo 1 > /sys/devices/system/cpu/cpu0/cpufreq/ondemand/ignore_nice_load
echo 2 > /sys/devices/system/cpu/cpu0/cpufreq/ondemand/ignore_nice_load
echo 3 > /sys/devices/system/cpu/cpu0/cpufreq/ondemand/ignore_nice_load
This will give the process created a nice value of 18, don't know if it will give all 4 a value of 18, but the first will be 18.
The magic here is '$!' which is the Process ID of the last execute program, in this case Folding client.