1.) Open console (With the key between 'Esc' and 'Tab').
2.) Type "!set ctype [element] [ctype]" where [element] is the "short" version of the elements name (Water is WATR and diesel is DESL, for example) and [ctype] is the element you want to set your ctype to be.
Example: If I want to set the ctype of iron to water I'd write "!set ctype IRON WATR".
3.) Press enter and then close the console with the same key you opened it.