Two basic options for overcoming region switching limits are 1) copy and/or encode the DVD to hard drive and play it from there, and 2) upgrade the DVD firmware.

Apple's DVD drives seem to have their own copy protection (?), so I use a third party DVD reader to copy DVDs to the hard drive. In System Preferences -> CDs & DVDs, I set "When you insert a video DVD" to "Ignore". Then I save my (purchased) DVD to disk with a program such as MacTheRipper, and view it by dragging-and-dropping the resulting VIDEO_TS folder onto DVD Player.

With a program such as HandBrake, I am able to encode DVDs using Apple's DVD drives. This creates a file which may be played in Quicktime, but quality suffers compared to the original DVD.

I have not tried upgrading my DVD drive's firmware since the above options work for me.