Enlarging window ROs in Gunnison Kit Home

I am looking into enlarging some window openings in what I believe to be a Gunnison modular kit home (https://instanthouse.blogspot.com/2012/01/gunnison-magic-homes.html). I am a little bit unsure about modifying this particular frame–cross-hatched on the flat studs sandwiched in plywood. Does anyone have experience modifying these or similar frames?
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pictures always help