In my heart was a desire to live more dangerously. I was not unprepared for jagged rocks and treacherous shoals if I could only have change - change and the excitement of the unforeseen.

1）In my heart was a desire to live more dangerously 是不是少了不定式的形式主语it, 即In my heart was a desire to live more dangerously ?

2)  if I could only have change 这里could是表过去的能力还是过去的推断呢？ 另外这里的only是加大语气“只能，别无他法”的意思吧？


1 In my heart was a desire to live more dangerously. 

这是一个完全倒装句，介词短语作表语前置，主语后移。不定式是desire的定语，不是主语。

2 could不是表示能力，更不是表示推断，而是表示客观条件允许，即所谓理论上的可能性。

if I could only have...= if only I could have..., 只须...， 引导条件状语从句，表示充分条件。