How does the Awakened Spellbook damage type replacement work, exactly?

Question

At 2nd level, an Order of Scribes wizard gets the Awakened Spellbook feature, which includes this benefit:

When you cast a wizard spell with a spell slot, you can temporarily replace its damage type with a type that appears in another spell in your spellbook.

So, can this feature do the following things?

1. Replace the type of damage dealt by a spell with a type another spell in your book at that level could deal. For example, a casting of Magic Missile could deal Poison damage if you have Chromatic Orb in your book. I think we can all agree this is a yes.

2. Replace the type of damage dealt by a spell with a type mentioned in another spell in your book at that level. For example, a casting of Fireball could deal Psychic damage if you also have Intellect Fortress in your book. (For bonus points: Does Feign Death's "resistance to all damage except Psychic damage" count? If so, can you change the type to Psychic or to any except Psychic?)

3. Replace another damage type based effect with a type mentioned in another spell in your book at that level. For example, a casting of Intellect Fortress could give resistance to Fire damage instead of resistance to Psychic damage if you also have Fireball in your book.

If you have any experience with allowing or disallowing option 2 or 3 in your game, please include your opinion on how that worked out.

Answer 1

Option 1 for sure. Maybe option 2, ask your DM.

When you cast a wizard spell with a spell slot, you can temporarily replace its damage type with a type that appears in another spell in your spellbook.

The idea here is to replace your spell's damage type by another spell's damage type.

DAMAGE TYPES

Different attacks, damaging spells, and other harmful effects deal different types of damage. Damage types have no rules of their own, but other rules, such as damage resistance, rely on the types.

1 - Magic Missile can deal Chromatic Orb's poison type damage

3 - Intellect Fortress has no damage type to be replaced; it instead has a resistance type (psychic)

You can double-check this in D&D Beyond, by filtering spells by damage type. The damage type of a spell is the type of damage the spell can deal.

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Regarding option 2, it depends on how you want to read the feature. I interpret it as "replacing with another spell's damage type", so Fireball cannot deal Psychic Damage from Intellect Fortress, since IF does not have any damage type.

However, it is ambiguous, and you can argue that this can be read as "replacing with any damage type as long as it is referenced by another spell". I don't think this makes much sense, but this feature is so situational that it shouldn't do any harm ruling this way. It is, however, up to your DM.