User blog comment:Jimeee/Skyrim 1.9 beta update adds Legendary difficulty and raises level cap (Updated Apr 8th)/@comment-68.34.93.59-20130409124322/@comment-4709478-20130409225953

Making a skill Legendary will not affect your total level (say, you make your smithing legendary, you'll still be level 43). It will, however, affect the skill that you've chosen to make legendary (say, you make your smithing legendary, it'll reset to 15, but not lowering your total level).