I'm not sure if you can do custom graphics, but it doesn't look like it. Sleeper Service has a note in CE that says "some drones didn't make the final cut...they didn't work as intended", and one of them looks like a shield drone.
Sleeper Service wrote:Currently, about 40 new drones are added to the game. Some of the drones that where planned didn't work as intended, they didn't make it into the mod and are sad now.
Somewhat related question for Sleeper: why didn't they work, and what were they meant to be?