Changing a First Language Permanently

Is it possible to change one's first language? What are the implications? In order to approach such a question, one needs to have a clear definition of mother tongue, first language, second language, stronger language, dominant language, etc. If you feel interested, see what Grosjean has to say about it.
http://www.psychologytoday.com/blog/life-bilingual/201210/changing-first-language-permanently