Can I change my race without affecting my vampire lord in Dawnguard? I don't care about skills, I just want to know about if it will affect my vampire lord ability.
While I can't vouch for the authenticity (Save first, then try!), I found these instructions that, while only made for a normal vampire, have a note about vampire lords.
If you are a vampire lord, you need a mod to prevent changing back into your old race. The game records what your race was at the time you get Vampire Lord form, and recalls that when you revert back. So it recalls your original, ORIGINAL form when you change back. The nexus has a mod that works for me.
To sum up the precedure (you should replace [current race] and [new race] with your current and new race, for example WoodElf or Breton, so the expressions become "WoodElfRace"):
player.setrace [current race]Race
player.setrace [new race]Race
Showracemenu //this is for changing your looks
player.setrace [new race]RaceVampire