Simple way to change messages after node creation
You can do it through Rules

Create a new rule configuration and set the event to Node | After saving new content.



Add a condition, Node | Content is of type and set CONTENT TYPES to Article, as shown in the following screenshot:



Add an Action and select System | Show a message on the site



By using the Action, After saving new content, we're asking Rules to react on content creation. This means that the rule will fire every time a new content has been created in the system. By using Conditions, we can tell Rules to only fire the action if the created content type is Article (or any other content type). In the MESSAGE field, we've used REPLACEMENT PATTERNS to insert chunks of data from the objects available in our current rule configuration.