Automate unchecking of "Charge tax on this product"

[edk]

We are a 501(c)3 nonprofit and do not charge tax on our products.  

But dozens of products were loaded onto the site and the "Charge tax on this product" box is checked by mistake.  Is there an app that can go through our inventory and clear that checkbox?  Or whatever mechanism it takes to not charge taxes on anything?  

And BTW is there a way to make that the default for new products?

Thanks

Ed K