Creating short cut for "Replace", "Find", "Advanced find and replace" Word for Mac

Here are the steps:

1. In Word, choose Tools>Customize Keyboard.
2. In the Categories list, scroll down to All Commands and select it.
3. In the Commands list, scroll down to EditReplace and select it.
4. Click in the Press new keyboard shortcut field and press your key combination. Ctrl + R is working here.
5. Click on the Assign button. OK out.

Test operation by pressing Ctrl and R at the same time. The dialog that opens is the Advanced Find and Replace dialog, but it opens to the Replace pane of that dialog. So you don't need a separate shortcut to get both.

The most likely cause is that you are attempting to use the Option key in the combination you're trying to assign. Avoid that or use it only in conjunction with at least one other modifier key. For example:

Option+n won't be recognized. Neither will Shift+Option+n. However, including the Control or Command key will be accepted.