Changing the Text in the Portal Breadcrumb Menu

I use the portal for case management, we have added a custom 'Case Number' field onto case which we want to use throughout the portal rather than the ugly OOB Case Number field. I've managed to figure how to hide it from *most* places except the breadcrumb menu/title in the browser tab. I've highlighted in yellow the bits I mean. I want these to reference the custom case number field. Where can I change this?