Can you actually change your Snapchat username now, and do you lose your streaks or friends?

Yes, Snapchat added username changes a while back and it's safe. Go to your Profile > tap the gear (Settings) > Username > Change Username. The good news: you keep your friends, Snap score, streaks, memories, everything, nothing resets. The limits: you can only change it once per year, and your old username can't be reused by you or claimed by anyone else afterward. Your Display Name (the nickname friends actually see) has always been freely changeable and separate, so if you only care about what people see, change that instead and skip the once-a-year username limit.