Hello,
you you shouldn't override the createNode operation on the NodeService. Technically it is possibly by injecting an interceptor into the public bean or sub-classin the DbNodeServiceImpl and overriding the private bean, but this would be an unsupported change.
What do you want to change in terms of behaviour? You should try to use any of the standard extension / customization methods for Alfresco, e.g. try using a Policy or Rule to achieve the desired behaviour…
Regards
Axel