When setting up a custom breadcrumb trail using the Custom Breadcrumb module you can determine whether the breadcrumb should be displayed by using a snippet of PHP to return TRUE or FALSE. This code has access to the $node variable, and can be used to check things like it's type, or in this instance what taxonomy term is associated with a node.
For this example we have a content type of Case Studies and when creating a node of this type there is an option to select what Category it belongs to from a list of taxonomy terms.
The Case Studies are displayed on different pages under their particular Category. Because of this we want to have custom breadcrumb trails leading back to the Category page a particular Case Study belongs to.
Creating the breadcrumb visibility rule
You need to check what Category value is associated with the Case Study you are viewing. Easiest way to find the correct syntax is by using the devel module - see this post about finding field attributes for more info.
Once you have found out how to reference and check the Category field value you will need to find out what the value is. In this example I'm using the TID of the taxonomy terms, and you can find this by going to the taxonomy list and hovering over the edit button - you will see something like this .../taxonomy/term/12/edit (tid=12 in this example).
You can then enter code similar to this in the breadcrumb visibility area to get it appearing for Case Studies tagged with that Category tid.
IMPORTANT - do not include the <?php ?> tags
if ($node->field_section['und']['taxonomy_term']->tid == 12) return TRUE;
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