it was in that room that the Republicans held.请问这里可以改成 it wa

不可以,这是强调句的典型句型.要强调的是“是在那个房间里”
我把强调句的句型给你看看：
“It is / was + 被强调部分 + that + 其它”.如 It is Tom that likes this colour. (强调主语) / It was my mother that I gave the present to yesterday. (强调宾语) / It was because I fell asleep that I missed the TV play. (强调状语) / It was into the schoolbag that he put his books. (强调补语)
注意：
1. 强调“人”的时候,也可以用who来代替that.如 It is Tom that likes this colour. = It is Tom who likes this colour.
2. 无论强调的是单数还是复数,都必须用“It is / was …”,不能用“It are / were …”.
希望我的回答能够帮到你,如有疑问,欢迎追问.O(∩_∩)O

还是有点区别的，it is/was....that是强调句的固定格式。
如果改用where 应该是. This was the room where... 这样才是定于从句；或者This room is where...表语从句。

可以

it was in that room that the Republicans held...
原句是一句强调句。如果要改成定语从句的话也可以的，只是起不到强调的作用了
it was that room where ...，如果先行词room在从句中做状语的话，这样改是对的
最好有句子让我看一下
有不会的可以再问我