You cannot cross the green safety-lines on the template. Everything not inside those lines will not be engraved at all. That's what they told me when I contacted them with that question.
I have another question myself:
I see the M100 Shadows come with the brushed metal shields. Are those matte or shiny brush metal shields? Or is there only one pair of shields included to that prize and I can choose that from the colors shown on the M100's page? Will they always come with those empty shields or can I have those engraved and then have another set with different color?
No, that shields that come on the shadow M100s are not a glossy finish.
Yes, if you order them from the V-Moda site you should be able to have the set that already comes on the headphones engraved, as well as the free set that they come with. But they are going to open the box in order to get the shields, as well as install them, so you will not be able to go through the ceremonial unboxing process.