Not a tax professional here but was the executrix for my parents' estate in 2023. My sympathies for your loss, I know how it is, having lost both my parents within two months of each other.
I can't answer your first question about signing the MI form (but I would guess Why not? I don't think it would hurt, but I'm in CT soooo....).
I'd send in a copy of the death cert - attach a note saying it's a copy of the original submitted in 2023 (don't give another original you paid $20 for, or whatever the charge is in your state), highlight the note message in yellow, anything to make it stand out. Don't assume the person processing your form this year has access to last year's forms easily. Give them no excuse to reject your filing.
Hope this helps.
Pao
