@horselessname using value mappings as mentioned in How to Rename Values in Grafana Using Regex-Based Value Mapping is the way to do this.
The transform will change the field name, but not the values. I see you tried using an override with a value mapping. To rename a value you want to select the field name Service Name in the drop-down for Fields with name. Then, add the value mapping override for the field values that you want to rename.