1)If I (were) not ill, I (would) go fishing with my younger brother.
2)She loves him (as if) he (were) her own son.
3)If I (had known) it, I (WOULD) have told you.
4)I (wish) you (had not) told the plan to your father.
5)You can listen to the music (as MUCH as) you like.
6)(If) you like it (OR) not, you have to decide what to do.
7)I studied hard in my high school days; (????) I would have failed the examination.
8)No (sooner had) he gone to bed than he fell asleep.
9)I'll lend you the money (UNDER) the condition that you return it within six months.
10)It's about time you (SAW) a Shakespearian play.
7) I studied hard in my high school days; (THOUGH) I failed the examination.
ちなみに、"if I was" とか "if he/she was" を、"if I were" とか "if he/she were" という風に、"was" の代わりに "were" と表現することは慣例として残っているのでおかしくありません。