@Override
			public void modifyPrivate(MergeProgram mergeProgram) throws Exception {
				Library library =
					mergeProgram.createExternalLibrary(libname, SourceType.USER_DEFINED);
				Namespace namespace =
					mergeProgram.createNamespace(library, parentNamespace, SourceType.USER_DEFINED);
				mergeProgram.addExternalFunction(namespace, label, address,
					SourceType.USER_DEFINED);
			}
The external function merger only detects and merges source differences when a name
difference is being merged.
Ghidra/Features/Base/src/test.slow/java/ghidra/app/merge/listing/ExternalMergerAddTest.java