Strongly recommend crafting Scorch ASAP then, unless you're a Monsters player in which case Succubus can substitute to some extent and you might have more pressing priorities. Scorch is one of the game's best spells. It's useful in any deck except those looking to play its own very-big units. It's further a neutral card, and it's silver making it relatively cheap to craft.
I doubt your change to Ciri: Nova would keep it viable. By forcing Ciri: Nova to be played as second-last card, you're very vulnerable to Scorch effects which you cannot beat unless you're going into the last round with card advantage (not likely). When a win condition can be answered this easily by a card as ubiquitous as Scorch, the deck is not likely to be competitive.
Finally I'd like to stress, don't look down on Succubus. The card's value waxes and wanes with the meta, but it was a completely competitive choice last patch (see https://www.gwentdb.com/decks/37155-succubus-to-gm-trancenergys-4-5k-eredin-list). With it you already have a card that can answer Ciri: Nova. Use it.
I doubt your change to Ciri: Nova would keep it viable. By forcing Ciri: Nova to be played as second-last card, you're very vulnerable to Scorch effects which you cannot beat unless you're going into the last round with card advantage (not likely). When a win condition can be answered this easily by a card as ubiquitous as Scorch, the deck is not likely to be competitive.
Finally I'd like to stress, don't look down on Succubus. The card's value waxes and wanes with the meta, but it was a completely competitive choice last patch (see https://www.gwentdb.com/decks/37155-succubus-to-gm-trancenergys-4-5k-eredin-list). With it you already have a card that can answer Ciri: Nova. Use it.