It not should be that hard to make particle editor vias LUA.
The only issue I'm founding is than there is not GG lua command to open and search the image file, so you has to type the image file name manually.
The rest well, I've take graphis snow script as start point.
If you notice all the values are passed directly in the script, ie: offset, speed, scale, snd so on; I've just declare globals, and pass those values via global vars.ie: speed = speed_s or 0,02 or whaever value you want to.
In the above example, the global var named speed_s
like the others takes their values via user_imput, that way you can edit particles in real-time. Just has to mime the GG properties panel (Gimp/ps) , make "textboxes" (sprites) in front of each one. and the user do the rest.
Apply mouse, put some buttons such as: Apply and Cancel, If user press Apply all those user values will be apply to the particle script.
Now I've some other priorities, but plane continue working with , when done.
Laptop: Lenovo - Intel(R) Celeron(R) CPU 1005M @ 1.90GHz
OS: Windows 10 (64) - Ram: 4 gb - Hd: 283 gb - Video card: Intel(R) HD Graphics
cpu mark: 10396.6
2d graphics mark: 947.9
3d graphics mark: 8310.9
memory mark 2584.8
Disk mark: 1146.3
Passmark rating: 3662.4