Kernel Settings topic

Hey Guys,
i have a question
Well how you mod your kernel e.g Render Kernel for more battery ?
Cause i can flast the render Kernel but didn't have a clue what i need to change in the Kernel settings with programms like synapse and so...
Also i didn't find a tutorial for moding the settings of a kernel

It would be nice if some one would provide me the basics of that cause as i say above i'm a noob in moding a kernel due to the fact that i didn't ever done it.

Thanks