I was going through the forums and someone mentioned that if you deny Lord Harkon's gift, Serana can give it you after the story ends and they mentioned that it's also a different appearance. So my question is; Can Serana make you a VL and does it look different than the normal VL?

Yes she can, no it looks the same

Yep. You can become a friggin' vampire lord. Even if you side with the Dawnguard. *Facepalms* I think it looks the same, but I'm not sure.

Edit: Ninja'd.

That's pretty stupid, tbh. Completely defeats the point of two storylines.

Pretty much. Dawnguard is the better faction because you get all the perks of being a VL in the end, and you get all the cool rune weapons and the crossbow/bolt upgrades.