请问,在什么样的情况下形容词修饰名词或代名词时可以后制?

可以！详细看看英语参考书！

当然可以。

someone/anyone/everyone/somewhere/anywhere这些词语都是不定代词，形容词或者副词词组修饰这些词语必须后置。

eg

There is nobody available in such a busy street.

Could you please provide me something helpful to tests?