There are several ways referred as being able to deal with dif region code DVDs, but if you switch yor drive the limit uses to be that and it probably will stay locked at te last change result.
There were some facilites for a particular brand (I guess it was Hitachi, but don't know for sure) that would allow you to reset that counter back to zero.
So being a counter, there must be ways to achieve it, but it can be considered not legal under your own Law.
Other way is via firmware to make your drive regio free - but here you face the same legal issues. Depending on the place you live, it can be allowed or not.
And you have the software solutions, one pointed out above but there are more around.
Sorry no experience on that, just the things I read around. If you search on the subject you will find a lot of info.
you can start having a look at www.videohelp.com
But at present prices, having a dedicated drive to read another region you have discs from will not cost you a fortune and you don't need to lock the one you have now.