Solution:
(define-key (current-global-map) [remap org-cycle-agenda-files] 'jump-to-register)
Explanations:
Remapping Commands
You can tell Emacs that you want to replace all
keys pointing to a certain command with one of your own choosing by
using the remap notation.
You must do this instead of passing a key to the key bind function you
are using. This is the best way of replacing existing commands with
your own, as Emacs does the hard work of figuring out all the keys it
needs to rebind.
Source: Mastering Emacs
EDIT:
Here is a preferable solution:
(define-key org-mode-map (kbd "C-'") nil)
(global-set-key (kbd "C-'") 'jump-to-register)