TurboTax says:
"[IRS} can still assess a penalty or charge interest for not paying the proper amount when the taxes were originally due."
IRS can waive a penalty but not interest.
Penalties:
Subtract any penalty from the amount you owe reported on original 1040.
Don't try to include, but ignore, any new or changed penalty.
IRS will calculate your new penalty on their own and will bill you.
