Sounds to me like you are trying to create Geo-Alchemy. Big Earth magics, mixed with trasmorgrative spells, to let shifts in form be permanent. With the addition of polish and cut to the jem, I would put this about as difficult as building a sparrow from scratch. Not impossible, but not a snap.
"Also, consider that the consequences and other aspects in those situations are often the
result of the spell, but they aren't
sustained by the spell. Attacks of that kind don't really
have an intrinsic duration--they just happen, and they're done."
(YS266)
I think there's a good argument that it's not even transformative since it's still the exact same number and type of atoms; only their positioning is changed and carbon is just as happy being diamonds as coal. I don't think you'd need to allocate even one shift to duration.
Yeah, it'd definitely take more complexity to arrange them in a pretty fashion but that's not really necessary if you can just pay a jeweler to do it for you or tell them lop off enough to cover the cost and keep it.