But I'll ask anyway.

if I have the Best Mod on, and have already given my character Beast Blood.

Will that break the Companion questline?

If it's a question about a mod, best to move it to Mods

Ah gotcha. Didn't think about that, lol

Do you mean something like Moonlight Tales(the Overhaul or Essentials versions), or another Werewolf mod? Those shouldn't really change much about the Companion quests, and thus should not break them.

I'm not sure what the vanilla game/quest would do if you were already a Werewolf when speaking to Skjor in the Underforge, but the http://www.nexusmods.com/skyrim/mods/22650/? mod adds a lot to the Companions questline, like more quests between story missions(although these are Radiant Quests) - and the story quests can require high enough skills and a certain level, a few added scenes(though the added lines are unvoiced), and I haven't seen it yet, but you can mention to Skjor that you are already a Werewolf in the Underforge, and he likely has something in response.

Ah okay. That's what I was asking, was during the underforge sequence, when they try to turn you into a werewolf, would I have a questline that I couldn't complete. I have Moonlight Tales