is it possible to change the values in a combo editor in a datatable?
Yes, it is possible to update the values displayed in the option list. Since it is a standard Webix list, all the list API works for it.
Depending on the situation, the object of an option list can be accessed by different methods. For instance, in the onAfterEditStop event handler it looks like this: http://webix.com/snippet/a4febc07
Handlers can be also set for the list itself. Maybe this documentation article will help you: http://docs.webix.com/desktop__advanced_combo.html.