How to customize node save message,

hello,
I am the new in the drupal, now i want to customize the drupal node save or update message "Your has been created\updated."
I know about the drupal_set_message function but its work twice for me, its gives me 2 message. 1 is my custom message and 2 is drupal's own message,
I c't change in drupal's core module, otherwise its effected in all node type module. i have 1 another way to remove the drupal's message. all messages are store into session. so first i need to remove form session then after set may custom message. this is last step for me.
Does any budy have new solution , remember i c't do any change in core module (node.module)