Currently the Style Override Highlighter [+] in the various styles panels functions as a toggle on a per app basis, not as an "on" or "off" preference setting. This means it can't be set on a document by document basis, as enabling it will actually toggle the setting to "off" if a user has the setting switched "on" in their copy of InDesign.

Would greatly appreciate the ability to set this as a normal InDesign preference - ie one that can be set at application/document level, the same as almost every other setting in the program.