Upvote:0
The Italian National Identity Card is a fully fledged identity document, released both to nationals and aliens (not these 👽).
It replaces the passport completely in order to identify an individual, e.g. when boarding a national flight, because it carries both photo and encrypted fingerprints of the holder. You are probably within the Italian territory already today, so it's not worth mentioning that the National ID for aliens is not a valid Schengen travel document (but the Residence permit is).
Traveling within the country to visit the Embassy is permitted with a valid National ID. If you skip air travel, it is extremely unlikely that someone will ever ask to see your ID/passport on your journey to Rome.
Upvote:2
If you have a valid Permesso di soggiorno, your stay in Italy remains tolerated despite an expired (or lost) passport, but you should obtain a new valid passport as soon as possible.
You have no restriction on where you can travel within Italy because of the expired passport. However, other restrictions may apply, for example, Covid-related restrictions may prevent or obstruct you from interregional travel, although replacing passport might qualify as a good reason for travel (on this I have no practical knowledge if it would actually qualify as an exception).