Spell generation question

You first change one of your 4's to 6, and then can still decide to take the signature spell.

BRB p. 490: "Otherwise, if you roll a spell twice (whether for the same Wizard or for a different Wizard in the army) you must normally replace the duplicate spell with another of your choice from the same Lore. If you cannot, because all the other spells have already been taken by other Wizards, for example, then this extra spell slot is lost."

Ibidem: "After choosing replacements for duplicate spells, a Wizard can always choose to substitute one of the spells he rolls with the signature spell of a lore — even if another Wizard in the same army already knows the signature spell."