You can call USCIS, say “info pass”, and request an I-551 stamp after your extension letter expires and when you need the extension.
now. Why pay for an I-90 and N-400?
I don’t recommend that. Name changes can
*lengthen the amount of time to take oath, or
* decouple the oath from the processing of the change of name document. The change of name document is can be delayed indefinitely. You can end up with no green card, and end up with a naturalization certificate in your new name that is useless without the change of name document. You are then effectively a non person.
Instead naturalize in your current name. Then change your name through state court.
Quicker and simpler.