Setting new keys in context with custom behavior

I am trying to add keys in a custom behavior with context.set(), but am not exactly sure how to return the context afterwards. For example, this does not update the context.

In the XML, I have a custom Behavior Module with the name modifyAnyDeliverableSelection

In application.js, I have something like

Sideview.utils.declareCustomBehavior("modifyAnyDeliverableSelection", function(module) {

    module.onContextChange = function() {

        var context = this.getContext();

        context.set('variable',"foo");

        return context;
    }

});

The context does not get updated. Am I missing something here? Is it not getting returned properly?