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Not really. If I nickname it BELDUM, it considers as if BELDUM was a nickname, and it'll not change to METAGROSS, or to the Japanese nickname when it evolve. I've tested it.
Okay, I'm adding you and connecting. The UT cames Nicknamed METAGROSS, because I was just stupid and NNed it just after hatching the egg, so I don't have an UT Not-Nicknamed copy.