FimFiction Link - Short ID: 9767/moonbeam
Published: Feb '12
This is a S1 SoL fic in which a changeling OC (given name Luna, like the moth) takes on the identity of one titular earth pony, and moves into Ponyville to make some friends and take up farming (really? A mare of her talents?). That seems to be what the author intended to write, anyway, and he did a great job with *that* story. There are a few reminders, from time to time, that Celestia and Twilight are searching for a missing Princess Luna, but they have very little impact on Moonbeam and her four background pony friends.
Even discounting the lack of characterization for S1 Luna, this "Luna" has basically no relationship with the character. She doesn't care about her royal status, much less her divinity. Celestia's importance is only that of a threat to her disguise, and she doesn't know the M6.
That said, this story isn't about showcasing the M6, nor Luna meeting them in turn as something that ruins many oldfics. Nearly all of the time spent on mundanities of background pony life and the fic is top comfy in this fashion. The fic takes place about two months after FiM and spans another few months over the course of FWF, WWU and finally OaB. The OCs are nice, the interactions are very cute, and all of the characters are adorably friendly with each other. Moonbeam is impulsive, very social and sociable, kind and empathic, she makes friends easily. One of the few issues with the story besides her not being Luna is that there's almost nothing to support the notion that she can't make friends in Canterlot, indeed, she is already friends with the castle librarian in Ch 1. This omission is papered over with some explanation at the end.