The only way would be to either add another condition to the formulas,
so that zero is returned, and/or change the referenced cells so that
zero is returned.
It's possible to make the cells **appear** as zero with a custom format
and NOT loose the formulas, but not "reset their values to zero", unless
using the method stated above.
I have to ask, why do you wish to do this? Perhaps there is a better
way.