Now, I want to experiment in Grub Rescue> shell. But I don't what deliberate changes I have to make so that I will be booted to Grub Rescue> shell on next reboot.
The quote above doesn't make sense. The way it reads, you want to get a grub rescue prompt but you don't want to make any changes to be able to do this? Contradictory wishes. If that what you want, you might need to contact a local magician. Or did you mean to have the word 'know' between 'don't and 'what'?
You get the grub rescue prompt if grub cannot find the grub directory, the kernel, the normal.mod or linux.mod files. So move one or more from their proper locations and make a note of where you moved it to so you can move it/them back.
Make sure you have detailed info on how to repair the problem before beginning, at least a Linux Live CD.