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Maybe the only way is to re-encode all movie.
Try to use DVD-Rebuilder, a free tool.
This require a MPEG encoder (TMPGEnc or Cinema Craft or other), a very fast CPU, and a lot of time, but give best results in quality.
I don't know if rebuilder is able to change region, but it's can done with DVD shrink. Once you obtained a DVD with rebuilder, then you can convert movie into region 1 or also in region free with shrink without any compression or transcoding