Blossom-Blessed Angel // Seed Suture

Creating a copy of a creature's prepare spell in exile ignores copy exceptions applied to that creature that would affect the copiable values of that spell. For example, say a player casts Croaking Counterpart (a sorcery that says "Create a token that's a copy of target non-Frog creature, except it's a 1/1 green Frog") targeting Diviner of Victory. The token copy of Diviner of Victory will enter prepared as a 1/1 green Frog creature, but the copy of Unwind History in exile will still be a blue sorcery. The copy of Unwind History won't be green, a creature, or a Frog, and it won't have power or toughness.

A preparation card is a creature card in every zone. For example, while it's in your graveyard, Diviner of Victory is a blue creature card whose mana value is 1. It can't be the target of Stingcaster Mage's triggered ability ("When this creature enters, target instant or sorcery card in your graveyard gains flashback until end of turn. The flashback cost is equal to its mana cost.").

Casting a copy of a prepare spell from exile isn't casting it for an alternative cost. Effects that allow you to cast a spell for an alternative cost or without paying its mana cost may allow you to apply those to a copy of a prepare spell cast from exile.