Why can't you translate it? It has no key so a simple translation as follows should work fine.
Code:
'OR' => 'OR-CHANGED!'
It's a common string through so your change maybe being overridden by something else. See the below blog regarding the new overrides feature which you can use to force your translation.
www.joomlapolis.com/blog/kyle/18701-language-overrides-have-arrived