Can Emacs differentiate between ctrl-r and ctrl-shift-r?

Question

I\'d like to bind Ctrl + R to \'isearch-backward and bind Ctrl + Shift + R to \'tags-apropos

Answer 1

Yes.

(global-set-key (kbd "C-r") 'isearch-backward)
(global-set-key (kbd "C-S-r") 'tags-apropos)

The way to figure out the answer to this kind of question is to do help on a key C-h k, and type the keystrokes you're interested in. What Emacs shows in the Help buffer is the string you can pass to the macro 'kbd.