How can I undo the “Do Not Ask Again” for using my home screen wallpaper as my lock screen wallpaper as well? I use an app called "Live Video Wallpaper" or LVW which is basically a live wallpaper that allows you to select a video as your live wallpaper.

I have no problem with it but I accidentally checked the "Do Not Ask Again" option when I was asked whether or not I'd like to use my home screen wallpaper as my lock screen wallpaper too before I pressed no.

Now I have the problem that I can't set my home screen as my lock screen as well. Before, I used LVW as my home then set my Galaxy S2 to use it as my lock screen wallpaper as well but now with the option set to "NO" and the default set to "Do Not Ask Again", I can't do it anymore since live wallpapers normally cannot be set as lock screens (LVW was my way to get around that).

Is there a way I can "Unset" that "Do Not Ask Again" option for using my home as my lock screen wallpaper as well? Sorry if I'm redundant.
Try resetting the default wall paper setting by following these steps (described for Samsung's 4.0; see also this question): 

Menu | Settings | Applications | All | TwWallpaperChooser | Clear defaults

If you also want to reset the settings of your wallpaper application follow these steps:

Menu | Settings | Applications | (said application) | Clear data