Can I access the DLC new content features in the main campaign?

I read that the Blood and Wine expansion adds mutations to the character page

I was planning on purchasing the DLC after finishing the main game, but if I can access the new features before finishing it then I might just purchase it sooner.

Are the new stories, quests, and mechanics in the 2 DLCs accessible before finishing the main wild hunt campaign or do you unlock them after (I assume, having finished it yet) defeating the wild hunt?

Solution 1:

They are available before finishing the campaign, however Blood & Wine is very high level (Minimum Level ~35, Hearts of Stone has a minimum Level of ~29 and you will be 28-30 after finishing the main story), so they are designed to be played after finishing the main story. You can use the additional features some way into the expansions.

So, if you do them before finishing the main story, you will grossly overlevel the battle against the wild hunt (you can expect to be Level 45-50 after Blood & Wine). I recommend finishing the main campaign, then Hearts of Stone then Blood & Wine, this will be smoothest transition.