Does mixing rulings from different madhhabs count as creating a new madhhab?

Answer

In teaching, fatwas, or court rulings, yes -- it creates a form of practice without legitimate authority. At the individual level, per the Shafi'i and Hanbali Schools, mixing positions is not creating a new madhhab as long as it doesn't occur within a single domain (e.g. one wudu or one marriage contract) or closely related domains.