Well, in the mean time you can do it yourself. Not editing world.sav, that's very not recommended. Plus I'm not sure it would work. But, if you set the number of regional interactions that are generated to 0, you won't get any random ones. Then you can roll your own, by making a bunch of variations of Toady's example.
Then you can have it raise them on a new moon, or even less often, if there is such a parameter.
But you don't want to lose the random rains and fogs? Well, I didn't say to set those to 0. But they're only assigned by regional interactions? So make some.
[OBJECT:INTERACTION]
[INTERACTION:EXAMPLE EVIL RAIN REGION]
[I_SOURCE:REGION]
[IS_REGION:EVIL_ONLY]
[IS_REGION:SAVAGE_ALLOWED]
[IS_REGION:ANY_TERRAIN]
[IS_FREQUENCY:100]
[I_TARGET:C:MATERIAL]
[IT_MATERIAL:MATERIAL:INORGANIC:EVIL_RAIN_1:WEATHER_FALLING_MATERIAL]
[I_EFFECT:MATERIAL_EMISSION]
[IE_TARGET:C]
[IE_INTERMITTENT:WEEKLY]
Yup, that actually works. You can have your hard-coded raw reference generated raws. Rains are EVIL_RAIN_#, and fogs are EVIL_CLOUD_#. Just make sure you don't create raws for more rains/clouds than your worldgen parameters make, or, unpredictable madness may ensue?
This will complain about missing materials every time you gen a world, load a save from that world, etc. But it works.