How do you get customs in marble blast gold

NOTE: In Mac, press F10, not ~ as mentioned below.

First, enter a level you wish to edit. Press the ~ key to bring up the command bar. Type in $testcheats=1; (don't forget the semicolon) and press ENTER. Press the ~ key to exit the command bar. Then press F11 to bring up the basic level making equipment. Use F4 to bring up the list of objects in MBG, and press F3 to change the object you have selected. Use the XYZ axis on a selected object to change its position. To take away something, select it (with the mouse, duh!) and press Ctrl Z.
You can select from a list of gems, hazards, basic level objects, and a bunch of other stuff!!!
To find out exactly how to get a picture for the level and the other things, go to this link: http://www.youtube.com/watch?v=YPmR7spHITI&feature=channel_page
Hope this helped! :D