I was reading the linux book which says this
Finally, if you break your kernel or boot loader, you won't be able to get to single-user mode without extra help. You can often boot your system with a kernel from a bootable CD-ROM by passing the root parameter to the CD-ROM's kernel boot loader. Your system might look somewhat strange without your regular kernel, but you should still be able to move files around or perhaps even compile a new kernel to get yourself out of the jam.
Now i want to practically do that and see how i can recompile the broken kernel from cd.
I means i have the running fine version of centos. I do something and my system won't boot as kernel gor corrupted.
Now can i recompile the kernel as said in book so that i can bring my system in running state. or my all chnages will be lost and data as well