or作为并列连词的用法向来简单而好理解,个人认为or在这里连接的是“for them”和“for them to do it for you”,这两个短语在这句话中都是作状语.
这句话的难点在于它的意思表达,尤其是后半句?我个人的理解是for them to do it for you,可以看成是for sb to do sth,那么后半句完整来看应该是You agree to do it for them to do it for you.这里for sb to do sth做目的状语,表示你这么做的目的,翻译成中文是,你为了让他们为你做这件事,同意做这件事.
整句话You agree to do it for them or for them to do it for you.的翻译是,你同意为他们做这件事,或者你为了让他们为你做这件事,而同意做这件事.太拗口了,但是意思应该就是这样.“for them”和“for them to do it for you”都是做表示目的的状语.
由此看来,肯定不能写成你想的那样.