When performing a find & replace operation on a large document, in which not all the found terms need replacing, one has to click repeatedly between Find and Replace buttons in order to skip or replace each found target depending on the surrounding textual context. Using the TAB/SHIFT-TAB combination allows the user to bypass the mouse/trackpad, but it is still very inefficient. A huge improvement would be to assign keyboard shortcuts to the buttons, which would alleviate considerably the strain on the user as there would be no need to slide the cursor back and forth all the time.
Under Linux and Windows, when Find & Replace dialog has the focus, I can use key F for Find and key R for Replace. Is it different on Mac?
After reading your comment, I tried the Command + F and R combinations, and indeed, these work on the Mac. I still think there should be a way to assign custom keyboard shortcuts, and not let each pane have a life of its own, as there are other problems such as reported in 46136. In the meantime, life got a bit simpler for me thanks to your post!
Due to Comment 2
After comment #2, this is more or less a feature/enhancement request, therefore I change the Summary to reflect this correctly.
So this would mean not only to have a Find&Replace key shortcut in Customize > Keyboard > Edit, but also one for "Find" and another one for "Replace" - these two only working as long as the Find&Replace Dialog is open. This is not specific for Mac so I changed the platform to "All"
It's common behavior: shortcuts are used to run commands (F1 = Help, Ctrl+S = Save) while hotkeys work within dialogs and focus the control or start the function. The look and feel depends on the OS (and desktop environment) and you may have to press the alt key to see the underlined character, which varies with the localization. In case of the F&R dialog you can also use the cursor key to go left/right and press enter to execute the function of the highlighted button. This is very efficient and does not need additional support.