If you have an established site/domain before and need to change to a new domain with same content chances are you may retain your ranking. However there is still a possibility you can lose it due to different keywords in the new domain however I did a recent change from blogspot domain to my own domain where the new domain is not related to my website but still can rank high in SERP.
If we register a new domain and redirect it to an old domain, will we get top rankings for the redirected domain.