When are you going to update Form 2210 to reflect the IRS changing the underpayment exemption from 85% to 80%?

In a similar vein, can I just take the turbotax-filled out response to Form 2210, checkbox A, cross out "85%" and just write in "80%" waiver and send that in?

The IRS must first approve TT's revised version of that form.

If sounds like Turbo Tax is waiting for the IRS to approve their update to 80%, but if you want to do it sooner here are the instructions from the IRS: <a rel="nofollow" target="_blank" href="https://www.irs.gov/pub/irs-drop/n-19-25.pdf">https://www.irs.gov/pub/irs-drop/n-19-25.pdf</a>

The changes to Form 2210, Underpayment of Estimated Tax by Individuals, Estates and Trusts, are scheduled to be updated in a release currently planned for March 29, 2019.