I completed the Questline but as the Dawnguard cause I'm too much of a good-guy (And I like being a WW..) I do wanna try out being a VL for a bit to get an achievement and was wondering if you can turn into a VL once via Serena (Or whatever her name is)?

Yes, you can become a VL on both sides

Yeah it's really stupid.

Yes you can. Serana will offer it to you infinite times.

You can but they will not accept you. And frankly there is good in the Vampire side.

Thx. All I rly want is the achievement. I'm not a fan of vampires.