This is correct but you will not switch back to stock kernel after boot.. just the same values (i.e. 600mhz). To swtich back to stock kernel you need to in terminal as root:

apt-get install --reinstall kernel kernel-flasher

I would also advice you too read the overcklocking wiki and this post by Titan.This overclocking thing is purely for power users and could be a bit tricky for someone not familiar with linux. Also a new kernel-power-settings have been released which have altered the way how to setup the overclocking.

Now you need to:
1. kernel-config show (to see your setting)
2. kernel-config save mydefault (to make the settings-file)
4. leafpad /home/user/.kernel/mydefault (open the file)
5. edit the settings for your likening..
6. kernel-config setdefault mydefault (make it default)

When reboot it will go back to the mydefault settings always. And do not make this settings unstable. Keep them in range.

to make a testing file you could.
1. kernel-config save mytesting
2. leafpad /home/user/.kernel/mytesting (edit the file)
3. kernel-config load mytesting

Now if it reboot it will go back to mydefault if mytesting fails.

You could also chose other presetings like the lv/ulv/xlv/ideal if you like but that you set up a little bit different from the above.

To see the kernel-config options you just write kernel-config without anything els in terminal.