I am extracting several parts of my private "Dawnguard Tweeks" module to pack into a mod I eventually intend to release; "Dawnguard Arsenal". One of the items in it is a sun damage rune which I dubbed the "Meridian Rune". I got it working and everything... but now comes the daunting task of re-directing impact data refs in its impact data set to a copied form in the new module with a completely different FormID.

There are a lot of refs in the IPDS, and I really am hoping that it's possible to script-copy them... Does anyone know what TES5Edit script would do the job?

Simplest method: Copy your existing Mod, and delete EVERYTHING you don't want. That way you don't have to change anything. I did some testing with this a while back, and it seems to be basically safe-- the only issue I found was the console would only read/write to the last loaded of the two Mods, but Skyrim itself handled them fine, since they actually would have different Editor Ids internally.