So what 's the value of the variable? do you want to make this variable into a input box to make a dynamic variable or something else?
I think there is other way to make this happened, but not adding the variable into the excel.
You can define the variable(for example, vtest) to some value. And in front-end, using if function : when the Metric Code = 107, then output is vtest.
Hope it can help you.