Disable a Custom Taxonomies default save mechanism

Like Bainternet suggested – remove_meta_box( 'tagsdiv-custom_taxonomy_id', 'post', 'side' ); to remove the default Metabox. If you want to still see the terms. Then re-register the metabox with your own custom callback.

This callback function can then mimic the function used to display the default metabox – but simply omitting any input forms /checkboxes which send any data.

The function you’ll want to mimic is: