Why is it that only for "zachar u'n'keiva b'ra'o" does the Gemara mention what the rabbis replaced when they translated the Torah into Greek? For all the other ones, it just said with what they replaced various phrases.
Good question. The RASHASH asks this question. He answers that the Gemara is emphasizing that the Chachamim changed only the phrasee "Bera'am" in Bereishis 5:2, and not the earlier phrase "Bara Osam" in Bereishis 1:27.
As for why they only changed the later phrase and not the earlier one, see the YEFEH MAR'EH cited by the MAHARSHA and RASHASH.