I can tell you that there are 2 sets of debris for Motion Debris, one is standard, the other is for Nebula (but for the longest time, the Nebula entries in the code were not specified and looped (if I recall correctly) using the non-Nebula ones, so I'm not specifically sure that it's utilizing any "different" ones in a nebula vs. not.
So it is possible to make a separate toggle for each depending, I'll admit though that it's been awhile since I've looked at it, so I don't fully know what it would require.
debris_vclip Debris_vclips_normal[MAX_DEBRIS_VCLIPS] = { { -1, -1, "debris01" }, { -1, -1, "debris02" }, { -1, -1, "debris03" }, { -1, -1, "debris04" } };
debris_vclip Debris_vclips_nebula[MAX_DEBRIS_VCLIPS] = { { -1, -1, "nebdeb01" }, { -1, -1, "nebdeb02" }, { -1, -1, "nebdeb03" }, { -1, -1, "nebdeb04" } };
debris_vclip *Debris_vclips = Debris_vclips_normal;