Can you please add this to your control.lua file, it will allow external mods to change the sprite in the display plate.

remote.add_interface(
    "DisplayPlates",
    {
        get_sprite = function(event)
            if event and event.entity and event.entity.valid then
                local spritetype, spritename = get_render_sprite_info(event.entity)
                return {spritetype=spritetype, spritename=spritename}
            else
                return nil
            end
        end,

        set_sprite = function(event)
            if event and event.entity and event.entity.valid and event.sprite and game.is_valid_sprite_path(event.sprite) then
                destroy_render(event.entity)
                render_overlay_sprite(event.entity, event.sprite)
            end
        end

    }
)

Sure, added in 1.3.0! Curious what you are making with this? 😄