日語 Japanese Ask Questions Thread2 質問

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Japanese - Ask questions thread
http://dis.4chan.org/read/lang/1174719097/l50

earlier it was mentioned how kanji onyomi merged like 作曲 was sakkyoku rather than sakukyoku and there was rules for it. I was wondering if there were rules for the kanji where the first letter in the second+ kanji take a different reading, e.g. 人々 is hitobito