Hero （as/though）he is ,the young soldier is humble and shy.

从你的疑问看出你不太明白这两句的意思.
Hero as he is,the young soldier is humble and shy.作为英雄,这位年青的士兵却谦逊而害羞.
Hero as he is = as a hero 这是倒装句
若用who 则要改为:
The hero who is a young soldier is humble and shy.
The young soldier who is a hero is humble and shy.
这句没法用 whom
Word spread here and there that the chemical factory near our school was pulled down.
我们学校附近的化学工厂拆毁了,这个消息传开去.
that 是引导句首的 word 的具体内容.
我猜你应为可以用 so 是因为你理解原文为：有些流传的消息速使我们学校附近的化学工厂拆毁了.但你若仔细分析原句的时态,就不难看出工厂拆毁在先,现在才有人在谈论此事.