Tried searching but couldn't find anything. Long story short, I got turned into a VL early in my adventuring life, joined the companions and turned into lycanthrope. I promptly went back to Lord Harkon right after turning and had him grant his gift again. He said something along the lines of "don't let me catch you losing the gift again".
I've read that Serana will grant the gift unlimited times but does she only do this at the end of the Dawnguard quest line or anytime you have access to meeting her?
Any difference between the "power" of the VL if Harkon or Serana grants it? I read something early on that Serana's version is weaker but that might just have been a rumor.
As this is leading to the whole face sculptor thing...