The law is silent as to installation charges, which arguably is a charge separate from the product price. (He did not actually demand the installation charge refunded on this call.)
I am not sure what "replacing the modified HVAC" entails, but if this is beyond the price of the refund, we may be able to argue this is separate as well.
In short, Legal proposes to attempt to require a signed release if we provide more than just the refund, but I anticipate he will just drop his demands to a straight refund (which he is basically at now) to avoid the signed release.