I want to set GRUB to boot up a particular option (eg, A different kernel version, different OS) when a certain key is pressed (eg, W to boot up windows with Ubuntu as default and L for Lubuntu). Is there a way to do this?
Not that I'm aware of. Is creating an extra line in the boot menu an option? In that case you select a different line in the boot menu instead of pressing W or L as proposed. But I guess you already have the two lines in the menu.
There is an option to automatically select the last choice you made.