Actually since they are technically separate units we could adjust the stats of the Dyson Gatlings without affecting the nebula scenario. The player controlled ones use the same stats as the nebula ones, and the nebula ones are NOT completely identical to the normal Dyson spawn. A key difference, the Dyson spawned Gatlings are immune to FF, the nebula ones are not.
I would say the best fit however would be to simply allow the gatlings to fire on ANYTHING that shoots them. This allows Fort IIIs and Superforts to easily shut them down without an issue, as well as high mark guardposts as well, but it wont be a complete shutdown from just Mark I & II posts.
The coding on it wouldn't be too hard either I think. Just remove the restriction from shooting at MKV units and Guardposts, add in one so they can NOT fire on anything that gives AIP (I think they have that anyway) and then set the Target Priority for Guardposts and MKV units to something really low. (Like the old Armored Warheads. So low that they just wont bother targeting those.) Finally, add a script that checks to see if the gatling is under fire, if so check to see if the gatling already has a target to shoot at or is just moving. If the gatling has a target, nothing happens. If the gatling does not have a current target and is just moving to a location/wormhole, then the thing firing on the gatling becomes its new target.
Yes this would potentially allow a fast (or long range), mobile unit to kite and destroy gatlings fairly easily, but that isn't much of an issue. They could do it before and most AI units don't autokite anyway.
While not everyone may agree with my solution, I do feel SOMETHING needs to be done. Because a single guardpost of MK III or less should NOT shutdown a 10/10 Dyson Sphere. When set that high it is SUPPOSED to be a significant impact on the game. And right now its not doing much of anything in almost every game I play. Even if I deepstrike in and knock out every guardpost from my world to the Dyson Sphere, unless I actually destroy every single AI command station all I have done is give it a clear path to attack me. Because it certainly wont do much to the AI.