I’ve seen some solutions out there that modify core code, some that just take a file and move it to your /app/code/local/ retaining the same directory structure, so as to just override the file. I don’t recommend either of these methods (especially the first), as with a true module you are setting up a much better environment over time for this to last. And a module allows you to ONLY override the methods you need to modify, instead of entire classes. Plus, you can easily disable the module right in the admin (Admin >> System >> Configuration >> Advanced).
Be sure you replace all of the “YOURSTUFF” with your name or company name.
I have only tested this with 22.214.171.124
Create the file: /app/etc/modules/YOURSTUFF_ImportMultipleImages.xml. This file tells Magento that you have this module and where it is located.