If you know you qualify for more deductions with the new unemployment tax break, would it be best to file an amendment after the IRS sends the additional refund?

yes. but only if your tax liability changes. 

YES ... that is exactly what the IRS says to do ... but WAIT for the corrected refund first.  Then you can amend the return that will probably take 6 months or much more to process ... don't expect anything quickly.  

Before you start make sure to save a PDF & .taxfile  of the original return  for safekeeping ... only then click on the amendment process.