Anyone know if NPCS in skyrim like those in solitude will attack if you become vampire lord using the way at the end of the bloodline mission where you get bit by Harkon in the castle?
According to the UESP article on Vampire Lords:
Vampire Lords are dangerous, fearsome creatures, and you will be attacked on sight if you are seen in this form. However, since NPCs will not recognize you, crimes committed in Vampire Lord form will not be attributed to you and will not increase your bounty. If you are seen transforming, 1000 gold will be added to your bounty.
Certain NPCs will never attack you, even when you’re in Vampire Lord form: children, probably carriage drivers, and anyone with a confidence of “cowardly,” for example. But you can expect city guards and lots of other NPCs to attack you on sight in Vampire Lord form.
If you accepted Harkon’s gift but are in your normal form, most NPCs won’t know that you’re a vampire, and won’t attack you.