The luna Guards are special and at least one community has a special connection with them: The tabetop gamers. This because they already know a light and dark version of the Pegasi species.

My own thoughts however are different. Do they really exist? We saw them only once, on nightmare night. And only two of them. We know Twilight was able to cast wings on Rarity so what can a Alicorn like Luna perform on two castle guards? It was nightmare night. What part of those ponies is costume and what is real? We also know that the Starswirl the bearded wing is under protection by night. -But from normal ponies with a dark fur.

If this species is existing, there must be only a few of them. Otherwise Luna would use them more.

By the way, do you know Blazing star? If you don't it's not bad. Nopony did know her on Brony fair, even she's one of the Bronycon mascots. But it looks like the Americans don't celebrate their mascots that much as we do. There's almost nothing about her around.