I hadn’t tried to understand the working of the GRUB2. One, day when my friend asked me how to make Windows the default entry in his GRUB menu, I didn’t have an answer. I went to the Ubuntu wiki page on GRUB2. Its very comprehensive. Most of the general aspects of the working of GRUB2 is explained in it, including the changes, how to configure the grub.cfg file, etc..
Though not explicitly stated in it, the method to make Windows the default entry was pretty clear from it. Here is how you do it-
2.sudo mv 30_os-prober 10_0s-prober
3.sudo mv 10_linux 20_linux
4.sudo mv 20_memtest86+ 30_memtest86+