custom marker in tree

Hi

I am trying to set a custom marker on a tree node to indicate the status of data in a related form.

I currently set the background colour of the icon when loading the tree, but need something that can be controlled dynamically once the tree has been loaded.

I have tried
a) changing the css element of the icon, but this changes as the item is selected/deselected.
b) defining #mark# in the template, but this only puts text in the descriptive part of the node, so wrapped this in a span and set a unique id. I could then change this span within javascript. Once again the webix structure overwrote the change.

As a last resort I could use the checkbox, but would like to use this for something else.
Is there a way of either creating another addressable element in a node that can be set/reset within javascript or of changing the css of the icon.

Your help as usual is much appreciated

SOLVED
I used a flag in the datastore and manipulated the folder:function accordingly
I just had not taken the option (b) process far enough by manipulating the data store directly.