Hmmm, a benevolent missile! Thats a very new and inovative idea! I can't ever remember someone asking a question like this before!
Anyways, looking into the Alphax.txt file where the aforementioned items are defined, why I think these two items are fixed. And as far as trying to duplicate/ modify these areas, why I think they are hardcoded, meaning they can't be modified thru any of the modible text files. FYI.
Now, as far as misiles causing more havouc are concerned, why you can build Scud Missiles with Nerve Agents via the Alphax.txt file. I usually make them available with Retroviral Engineering. I've also built an ICBM with a range of up to 30 tiles/ turn. I'm still deciding where the best place in the tech chart is for this item.
D