Update Multi-Choice Field Options with Pipeline (or other options)

I'm trying to figure out how to update options in a multi-choice field using a pipeline.  I'm open to other automated/scripted ways to do this.  Any help would be appreciated.

Ultimately, I'm looking to add a value to the field whenever a new, unique values is added via a relationship.  My reason for wanting to do this is to use the multi-choice field in the 'groupby' field in the Kanban report, which doesn't seem to accept relationships in that particular setting.  

Thanks!