Or just use this 'Find Replace in Selection' Automator Service (Dropbox download) without having to fuss about taking columns out to another app, fiddling with them there, and bring them back in.
It is just a short AppleScript that, after a quick installation, will look like this in your menu:

Select the cells where you want to make the replacement, choose 'Find Replace in Selection' from the menu, and enter the find-replace values when prompted. In your case you will see something like this:

Hit OK and you're done.
One-time installation is just a doubleclick on the .workflow package.

Depending on your settings you may have to go to System Preferences > Security & Privacy and click 'Open Anyway'.
'Install' simply moves the script to your Library > Services folder so it will show up in your Numbers menu. It doesn't do anything to the innards of your computer. If you want, you can check out the script first by choosing 'Open with Automator'.
Since this (obviously) changes values in your document you might want to test it first to make sure it is working as you want.
If you need to get rid of it then in Finder hold down the option key, choose Go in the menu and navigate to Library > Services, where you can trash it the way you would any other file or package in Finder.
SG
Edit: use jpg and nef rather than .jpg and .nef.