If the number on the form comes from a worksheet, you have to edit the source worksheet, you can't directly edit the form, even with override. I don't expect that to change.
I'm not sure why you are using Turbotax if you want to enter everything manually, using override voids all theTurbotax guarantees. You can use IRS "Free fillable forms" to manually prepare a tax return and e-file it. I don't think Turbotax is designed with users like you in mind. (Just my opinion and observation over many years.)
