So let me elaborate on this question a bit with an imaginary scenario: John is a young, recent Ph.D. graduate in computer science. During his Ph.D. he was mainly concentrating on network science and algorithms, but he has developed a deep interest in computational social science, a related but not that closely related field. He wants to get deeper into this and even perhaps change his primary area to computational social science, but he may not be prepared for this. He has read sufficient materials and research work about this, and the required technology/math for him is not difficult, but he hasn't done any real research on this subject.
So in this scenario, what should a young scholar like John do if he/she is really dedicated to making some contributions? Please note, that we are talking about a young scientist, not a tenured professor who has much more freedom.
A postdoc is certainly an option, but how likely is John getting a postdoc position since it's not his primary research area?