How do I change wallpaper real time regedit commands?

if i'm going to use Display Properties, it'll show at once. what i've noticed is that changes will take effect real time if it's a .bmp file and not for .jpg images.

That's because Windows does not support anything but bitmaps for the wallpaper (yes, even in Windows 7).

When you set a jpeg, gif, png, etc. as the wallpaper, Windows first converts it to a bitmap, saves it to a temporary file, and sets the wallpaper to that file (in Windows 7 the filename is more indicative of this):

In Windows XP: %appdata%\Microsoft\Internet Explorer\Wallpaper1.bmp
In Windows 7:  %appdata%\Roaming\Microsoft\Windows\Themes\TranscodedWallpaper.jpg

So I'm afraid that you will indeed need to first convert it to bitmap.