Typically a drop-down control is managed by the component's JavaScript. You can populate a drop-down control by using a JavaScript method. See this community article to learn how to create an AEM component with a drop-down and populate it using JavaScript:
http://helpx.adobe.com/experience-manager/using/creating-custom-xtype.html
You can dynamically update a drop-down list by calling an OSGi bundle operation. But in this use case - the OSGi bundle operation returns a data set that is displayed in a drop-down control - it does not manage it.