The examples cited are not mistranslations by the NWT, since they deal with logical possibilities within the meaning of the Hebrew words cited. And any translation, whether literal or not, should take context into consideration. Further, a literal translation from one language to a completely different language family -- for example from the Semitic branch of languages (Hebrew) to the Germanic/Indo-European branch (English) -- will have to merge its literalness with explanatory terms to bridge the differences. Otherwise, you do not have a translation, but an interlinear.
Jewish commentators, who certainly understood the Hebrew language, have long explained Genesis 10:9 to mean that Nimrod was a "mighty hunter before [literally, "in the face of"] YHWH" in the sense of a rebel against God. According to the classical Jewish commentator Rashi, "lifnei YHWH, it was his intention to provoke Him to His face. He captured the minds of people with his words and misled them into rebelling against the Omnipresent."
"In opposition to" is a legitimate rendering of the Hebrew preposition[lifnei, since the grammars demonstrate plainly that it can have a hostile sense (Exodus 20:3; 1 Chronicles 14:8; 2 Chronicles 14:9, etc.), implying defiance and opposition. (Brown, Driver, Briggs; Koehler & Baumgartner, etc.)