You can do that in Window menu -> Core configuration -> Custom commands, or in the corresponding window for individual games. The first input field is a command to execute before, the second to execute after. For that specific case the commands would be something like: Code: kernel-config limits 250 250 Code: kernel-config limits 500 600 or whatever other frequencies you want to use.
kernel-config limits 250 250
kernel-config limits 500 600