Alter field content inside modules hook_node_view
In HOOK_node_view() you can alter your fields like this:

function MODULE_node_view($node, $view_mode, $langcode) {
  //be sure to be in full page mode, but you can also user 'teaser'
  if ($view_mode == 'full' &amp;&amp; node_is_page($node)) {
    //kpr($node); =&gt; use devel module and kpr() to inspect your node.
    //Change the title of the node
    $node-&gt;title = 'New title';

    //Change the "text" field 
    $lang = field_language('node', $node, 'field_text');
    $node-&gt;field_text[$lang][0]['value'] = 'New field text value';

    //Change the "body" field which has a slightly different syntax
    $lang = field_language('node', $node, 'body');
    $node-&gt;body[$lang][0]['value'] = 'New body value';
  }
}


Note the usage of field_language() to retrieve the correct value for each field.