You might be interested in using the AML editor, sense AML still works in iC6. Grab it here.
http://developer.reallusion.com/amleditor.aspx

Or check out some documentation here.
http://www.reallusion.com/iclone/help/amleditor/

You'll need to open the resultant AML's you generate, and take the "$" signs out of the motion file path names. The "$" sign was a wild card. When you add your own files, they will be absolute paths, so you won't need the wild card.

The existing personas are in AML, and can be opened directly in this program. They only get saved as Lua when exported from iClone.

It has been four years since you said you were working on it... any updates yet?

Hi, All
Where can I find a guide to programming Lua script iClone?

Hi what are you looking to add a Lua to? Prop or Character?

I'd like to use it for both, if possible.

I mean, is it possible to use them on characters and props... are there scene controls, too?

Certainly on props.The perform commands are Lua's
They are easy to create using the time line.
Very simple lua
load  a box move the time on say ten squares then move the box.
If you now press play the box will move.
To repeat this action-Enter the time line select your box-transform.
On the line that says collect clip-
You will see two white dots.
Drag the cursor back from the second one to the beginning whilst holding the left mouse button.
Right click on the highlighted rectangle you've created and select add to perform name it whatever 'move box,
You have created a lua.
Now remove animation from box-Right click and select perform The Option 'Move box will appear.
Hope this was useful.
Cheers the Crank
PS you can create motion / Performs for characters in a similar way.

You can vote for access on RL's Feedback Tracker here.

I'd definitely find it useful to create custom controls such as iclone's light tool.