Editing point clouds

Since the cloud can be written in pdc format, and since sj_pc_write can be also used to convert pdc to mrmap, it is possible to edit the clouds.
I am not confident enough in Maya to suggest you how to do it, but I am pretty sure you can.
Let's see how to do it in Softimage.

We start from a very easy scene, rendered at a very low resolution (200x160) just for documentation purposes.
The pdc is written at c:\temp\sj\green_red.1.pdc

Now select File->Import->SjPdcImport , with c:\temp\sj\green_red.1.pdc as argument, and you should get something like this (I removed the mass and velocity setters, are they are not needed, and raised the particle size to 0.1

What we want to do is turn the green points to a light blu. As you can see above, the green sphere was tagged 4, and we can retrieve that info to change only those points.
The first thing you must do is set the Long0 attribute name to "tag". This way, the long0 port outputs the tag of each particle.
Also, set Vector2 to "normalPP", the attribute name of the normal in the input pdc file.

We then compare the tag (== Long0) with number 4, and if it's equal, we set the particle color to blu, and we leave it unchanged otherwise.

(Of course you can do much more interesting things)
We are now read to write out the new pdc. With the ice tree selected, pick File->Export->SjPdcExport, set the output name (c:\temp\sj\blu_red.1.pdc), the Long0 attribute to "tag" and the Vector2 attribute to "normalPP". Connect the two ports named Long0 and Vector2. This way, both the tag and the normal are preserved in the output file. Finally, connect Set Particle Position at the bottom of the ice execution stack.

We can now render the new pdc. Apply sj_write as camera shader, and set mode to Convert pdc to mrmap.
In this example, the output map is c:\temp\sj\blu_red.1.mrmap.
The same path is given to the sj_read shader applied over the grid.
After rendered once, the mrmap is created, and the lens shader can be muted or deleted.