Usually the English word "apostasy" is related to the Hebrew word "meshuvah," not "chaneph."
The WT Society is apparently basing their English choice of "apostate" on the suggestions posted by Lexicon in Veteris Testamenti, by Koehler/Baumgartner (Page 317).
In this Lexicon, they indicate the following relation to "chaneph" by defining it:
"be polluted, be inclined away from the right relation to God."
"pollute" .... lead to apostasy... alienated from God."
The Gesenius Hebrew-English Lexicon defines the adjective as "profane, irreligious...oft. heathen, apostate." As a substantive: "godless man."
Also, the Theological Wordbook of the Old Testament defines the word as:
"be defiled, polluted, profaned, corrupt."
"The core notion is of inclining away from right..."
"The adjective denotes a godless man, a man who forgets God (Job 8:13) and lives in opposition to all that is right..." (Vol 1, p. 695)
Therefore, the notion that "chaneph" can include the meaning of "apostasy" in some contexts seems possible. However, that does not mean necessarily that the NWT is justified to replace "godless" or "hypocrite" with this word. The Society appears to be pushing the pencil here in order to justify their repeated warnings to active JWs to stay away from "apostates."