Defining MagewrightsMagewrights could be written up as a Professional Edge, but I think leaving it as a title for an archetype would be good enough. One could suggest that a magewright is simply a character who only has the Arcane Background (Weird Science) Edge but not the Gadgeteer Edge.
Defining SchemasFor schemas, we simply create a new magic item called that is something of a mix between a scroll and tome (see Treasure in the Savage Worlds Fantasy Companion) that doesn't disappear after use (note: tomes don't disappear, but scrolls do). In other words, a schema is a scroll for creating a device, but acts as a tome in that it effectively gives a new power to the character who uses the schema; however, the character cannot recreate the device if the schema is lost.
I'd also require a character to have the Arcane Background (Weird Science) Edge to understand the designs and notations of schematics rather than allow anyone with any Arcane Background to use it as this would maintain the distinction of its function and flavor.
Here is the final result written in the context of Eberron:
An artificer or magewright can create a schema just like any other device using the Arcane Background (Weird Science) Edge. Only an artificer may use the Gadgeteer Edge to create a rough draft of a schema with the limitations inherent to the Gadgeteer Edge itself. An artificer or magewright may duplicate a schema with a successful Weird Science roll.