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If JC ever got turned into a woman I think he would end up looking like his mother, not sure what he would think of that (or WWX) but I doubt it would be nice.
I think he'd be a slightly softer clone of her, thanks to the influence of Jiang genes. Jiang Cheng loved his mother very much, so seeing her again in his reflection would be bittersweet. Personally, I think this would lead to him trying to arrange his hair like she wore hers; but since she had two handmaids who likely styled it for her, I think he'd end up frustrated and stuffing it into his usual bun.
Wei Wuxian canonically thought she was super hot, and he's a bi mess. Since her last words to him were "I hate you" and he can't distinguish between Yu Ziyuan and Jiang Cheng, he'd proceed to rewrite his memories even harder. But only after sneaking around so he could catch a glimpse of his hot little shimei. And probably saying "wow, Lan Zhan, did you think Jiang Cheng could get prettier? Hahaha, it's too bad about his personality" while Lan Wangji fantasized about throwing Jiang Cheng down a well.
More importantly, Jiang Cheng would definitely realize he could get pregnant two minutes after his body was changed, and then he'd be an agender king about it.