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I have an LG WH14NS40 (UK version) and I'm looking at getting Insomnia (2002) on Blu-ray, but it's only available as a US import so the disc is Region A. If I were to get it, would I be able to rip it regardless of the region or does that matter when ripping?

Yes, you will be able to rip the disc, region code is defeated. I frequently purchase discs from different regions and have always successfully ripped.