Flashed Note 2. In need of answers PLEASE topic

Hello. I had a phoned flashed from sprint to verizon. Sprint phone originally, but now running on straight talk verizon network. Anyway I was wondering if I could flash a rom to it?? To system update my phone?? Without ruining the flash of course. Any help would be appreicated because I am a noob. Please help!!!!!!!!!!
Thanks in advance:)

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