Yes, there are two complementary approaches. We can include other struts.xml-format files from a bootstrap struts.xml file, or we can package a struts.xml files in a JAR. Or both.
By Include
See the <include> element documentation.
You can use <include> elements in your struts.xml interchangeably with <package> elements. The configuration objects will be loaded in the order of appearance. The framework reads the configuration from top to bottom and adds objects as they are referenced.
By JAR
A "module" can be added to an application by placing a struts.xml and related classes into a JAR on the classpath. FreeMarker and Velocity templates can also be provided by JAR, making it possible to distribution a module in a single, self-contained JAR that is automatically configured on startup.