How do I alter a way node is rendered so I can add custom links/buttons? Sometimes I want to add custom links/buttons specific to a content type to a node when the page for that node is rendered, how would you achieve this when you write a module? An example code to achieve this by adding hello world link somewhere in the page when a node is rendered would be appreciated as the lack of documentation I can find for this is discouraging.
The easiest way to do this would be to use Content Templates!

Using this module you can have some fine-grained control over how templates and individual fields are displayed without actually creating a new .tpl.php file for that node (which is another pretty good much more laborious solution)