ANSWER:
If you mean that he follows only his whims and desires and he comes up with weird opinions that are not part of the 4 schools of thought, such a person is deviant and he is ignorant.
But if he is knowledgable yet he chooses only what goes along with the Quran and Sunnah but doesn’t go out of these reputable schools of thought, then this is permissible providing he is a scholar or a prominent student of knowledge.