For v2.8.3 the following should work:
YAMLFactory yf = new YAMLFactory();
ObjectMapper mapper = new ObjectMapper(yf);
ObjectNode root = (ObjectNode) mapper.readTree(yamlFileIn);
// modify root here
FileOutputStream fos = new FileOutputStream(yamlFileOut);
SequenceWriter sw = mapper.writerWithDefaultPrettyPrinter().writeValues(fos);
sw.write(root);