No, you can’t use higher circle slots to memorize lower circle spells. The reason why it isn’t allowed is related to your other questions.
If an Elf Ranger doesn’t take the ability that allows them to cast a certain circle of spells, they do not have access to it, even if they later gain access to a higher circle. To be able to learn a spell, a character must be able to cast spells of it circle (pg 42 “Known Spells). Since the character can’t use their higher circle slots to cast lower circle slots, they still don’t meet the requirements to learn spells of the circle.
Similarly, in order to cast a spell from a scroll, a character must be able to cast spells of that circle (pg 43 “Scrolls”). Since the Ranger still can’t cast spells of that circle, they can’t use scrolls from it, even when they gain the ability to cast higher circle spells.