You'll need to find the unit name that the computer understands (called the dictionary name) for this unit.

Find the export_descr_units file in the Data folder (or your mod's Data folder), and then do a search for Spartan Royal Guard. Once you're there, find the entry that starts with the word "dictionary". It ought to be immediately under the found text.

Then, use this dictionary name (with the _ characters) and see if that does the trick.