part.setDirty(true);

@Persist
public static void savePart(MPart part){
// In this area, parts that are set to be saved is here, so you can get the part and do whatever data saving you want
part.setDirty(false); //don't forget to mark this as false again!
} 

@PersistState
public static void beforeDisposePart(MPart part){
//Optional: in this area, if you still want to get the parts that are set NOT to be saved 

if(part.isDirty()){
//Do something here
}

}

part.getTags().add(EPartService.REMOVE_ON_HIDE_TAG );