There are unconfirmed reports that many of the Russians in an attempted Kursk counter attack were wearing Ukrainian uniforms, which is why they managed to get so deep into Ukrainian occupied territory before being repulsed. I wonder what would happen if, say, a bunch of South Korean volunteers were dressed in North Korean uniforms and dropped in the middle of the Russian lines? I imagine it wouldn't take too many, or too long, before the Russians and North Koreans are shooting it out.
Russians Disguised as Ukrainians Attempt to Seize City - Newsweek
And a video making the same claim: