[ic] Redefine variable

[Chad Wittrock]

Is there a way I can redefine a variable within IC? I would like to redefine
[shipping] from its default to :
	[set total_shipping]0[/set]
	[item-list]
         		[seti total_shipping][calc]
              	[scratch total_shipping] + ([item-field shipping] *
[item-quantity])
         		[/calc][/seti]
	[/item-list]
	[set shipping][scratch total_shipping][/set]

Where do I find where [shipping] is defined or is this not possible?

Any help is appreciated
Chad