Customize the way CCK Node Reference fields are displayed in Drupal

Node reference fields in Drupal are displayed as lists by default. Is there a way to change that?

I'd like to output them as JSON so I can create a fancy Java开发者_如何学编程Script visualization.

You can modify it in 2 ways: via custom module with function hook_form_alter or via theming (preprocessing form or templating form).
http://api.drupal.org/api/function/hook_form_alter/6
http://www.lullabot.com/articles/modifying-forms-drupal-5-and-6

For AHAH: http://api.drupal.org/api/drupal/developer--topics--forms_api_reference.html/6#ahah
Also, nodereference already have little ahah: "autocomplete" in field editing of custom node type.

Consider the Content Templates (Contemplate) module. Here is a quote about it (from the module's project page):

... allows modification of Drupal's teaser and body fields using administrator defined templates. These templates use PHP code and all of the node object variables are available for use in the template. An example node object is displayed and it is as simple as clicking on its properties to add them to the current template.

This module was written to solve a need with the Content Construction Kit (CCK), where it had a tendency toward outputting content in a not-very-pretty way. And as such, it dovetails nicely with CCK, adding a "template" tab to CCK content-type editing pages and pre-populating the templates with CCK's default layout. This makes it easy to rearrange fields, output different fields for teaser and body, remove the field title headers, output fields wrapped for use with tabs.module (part of JSTools), or anything you need.

But Content Template can actually be used on any node type and allows modification of the teaser and body properties before they go out in an RSS feed, search index, or are handed off to the theme. Additionally, ConTemplate can choose to add any files, images, or other media to RSS feeds as an attachment.

Templates are normally stored in the database but it is also possible to create disk-based templates which live in your sites directory and can be inherited across multisite installations in the same way as themes or modules.

Try the Custom Formatters module, simply make a custom formatter to render the node out exactly how you want it, then output the formatter to code or to a Feature for deployment.