Do you mean selling it to an NPC or selling it to other players? If it’s the latter I’ll go ahead and put this out there: if you have a ton of excess engram points, that means anyone near or above your level also has a ton of excess points. That would mean that your only prospective buyers would be low level players, who wouldn’t have anything worthwhile to trade. If you mean selling it to an NPC, I imagine it would be quite possible. Especially easy if you’re making items that only needed to be made once, like crafting stations (because then you could just make an item with an engram that costs X points and then is free to make without materials), but consumables or materials would be harder, but still probably doable. The problem is, what would be the point of this? Knowing that every single engram is learnable at level X, you could just make it so that at level X+n you learn something new, either something you made yourself or a mod item that is restricted until that level.