I'm...a bit surprised that it was only at post 13 that someone actually said 'no.'
Five million dollars is a good pile of money, but Jesus, think of the can of worms you just opened to get it. Every piece of identification you own is now, at best, completely invalid. Even your birth certificate is wrong. Real-world transexuals have problem enough with that sort of thing, and you're getting aliens involved in the whole ordeal. How long is that going to stay quiet?
In my life alone, I've already got a sister, so I pretty much know what I'd look like if I chose 'yes.' But gender amounts to more than just what you use when you want to take a leak. It-
Wait, why am I going this far into it? For me, probably not. Five million is a good deal of money, but I don't think it's worth the complications. If it was a "change your gender for X amount of time," my answer might be different, even if it were a lower quantity of money, but as it stands? Nah. Too much for too little.