Change content of a node
You can only use hook_view() when you are implementing the code for the module that defines a content type. 


  Display a node.
  
  This is a hook used by node modules. It allows a module to define a custom method of displaying its nodes, usually by displaying extra information particular to that node type.


The documentation of hook_view() for Drupal 7 is clearer:


  Display a node.
  
  This hook is invoked only on the module that defines the node's content type (use hook_node_view() to act on all node views).


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If you are writing code in Drupal 6 to alter the content of a content type implemented by another module, you can only use hook_nodeapi('alter'), for which the documentation reports:


  "alter": the $node-&gt;content array has been rendered, so the node body or teaser is filtered and now contains HTML. This op should only be used when text substitution, filtering, or other raw text operations are necessary.


As what you are trying to achieve is text substitution, this is the hook you should use.

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The equivalent for Drupal 7 is hook_node_view_alter().


  Alter the results of node_view().
  
  This hook is called after the content has been assembled in a structured array and may be used for doing processing which requires that the complete node content structure has been built.
  
  If the module wishes to act on the rendered HTML of the node rather than the structured content array, it may use this hook to add a #post_render callback. Alternatively, it could also implement hook_preprocess_node(). See drupal_render() and theme() documentation respectively for details.