▲to be discussed 在这里是不定式作定语吗？

答：你说得对，句中的 to be discussed 在这里是不定式作定语。

▲句中的to be discussed 改为 will be discussed 是否句意不变？

答：句中的to be discussed 不可以改为 will be discussed。但可以改为含有 will be discussed 的定语从句。即：

There are more than fifty proposals to be discussed at tomorrow’s conference.

=There are more than fifty proposals which will be discussed at tomorrow’s conference.

▲更多类似例句：

1. The carpets to be cleaned are in the garage. 要清洗的地毯在车库里。

= The carpets which will be cleaned are in the garage. 要清洗的地毯在车库里。

2. She made a list of the people to be invited. 她开了一个应邀请人的名单。

=She made a list of the people who will be invited. 她开了一个应邀请人的名单。

▲知识拓展：

上面说的是一般情况，根据具体的语境不同，有时不定式作定语并不一定表示将来。比如：

1. He is the second man to be killed in this way. 他是第二个这样死于非命的人。

=He is the second man who has been killed in this way. 他是第二个这样死于非命的人。

2. The unknown is always something to be feared. 未知的东西总是一种令人害怕的东西。

=The unknown is always something that is feared. 未知的东西总是一种令人害怕的东西。