I have already become a vampire through regular vampire bite. I would like to be able to become a vampire lord. But I am unable to progress the Dawnguard quest in order to rescue Serana to meet her daddy (which would not make much sense anyway...) as the Dawnguard attack me on sight.

Is it possible to become a vampire lord another way? If not in game, then is there a mod/console method for doing so?

Aside from a console command I dont think theres anyway. Why not just cure yourself then start the Dawnguard quest?

Player.addspell 0x00283b

The x is the number the Dawnguard esm is on the load order (usually 2 but if you have other mods with esms it could be different).

That aside it's odd that people at fort dawnguard attack you on sight, my experience is that they don't even know you're a vampire until a certain point in the quest.