The Short Answer
Yes, you can.

The Long Answer
The word “expatriate” (“expat” for short) describes someone living outside of his/her home country. However, people tend to use the word in different ways. Most people use “expat” to describe people from wealthy countries who move abroad for work, love, or inspiration rather than people who move to other countries to improve their lives. Back in the day, the word had certain connotations with exile (either voluntary or forced). For some people, the term “expat” conjures romantic images of artists like T.S. Eliot and Ernest Hemmingway carving out new territories and finding inspiration in distant countries.

A lot of people who live abroad never stop being expats, even when they live abroad for many years. That association with exile lingers, and there’s always that nagging feeling that “home” is somewhere else.

You stop being an expat when you start to view your country of residence as your “home” country. If you no longer feel like you live “abroad,” then you aren’t really an expat, at least not in my opinion. It probably helps if you take on citizenship or have dual citizenship in your country of residence, because if you do, the state doesn’t really view you as a “foreigner.”* A resolve to stay where you are and a lack of desire to move to your birth country also helps.

Not everyone gets there, but I’ve known people who have. I’m one of them.
I saw myself as an expat for many years. Heck, I still refer to myself as one on this blog (mostly because I’m far too lazy to change it). “Home” was Canada and I always felt like I was more Canadian than German, despite the fact that I chose to live in Germany over the long term. But something has changed over the past couple of years. I’m at the point where I’ve spent almost all of my adult life in Germany. I’ve also lived here for over a third of my life in total. More often than not, Germany is my frame of reference. I might complain about things here and make comparisons to Canada, but that doesn’t change the fact that Germany is “normal” to me. When I come back to Berlin after a trip, I’m coming home, even if I left to visit family in Canada. If I refer to “we” in terms of nationality, I can mean either Germans or Canadians (this confuses a lot of people, by the way).

A part of me will always be a little bit “foreign.” I have a noticeable accent in German. I’ll never think dubbed movies are quite as good as the real thing.** I will never like bread without some kind of butter or sauce to accompany it. At the same time, I think I’ll always feel a little bit foreign in Canada, and not just because I throw German words into conversations on a whim. I may not have spent my childhood in Germany, but I’ve been here for a long time and it’s part of who I am. It’s my home.

I guess that you stop being an expat when you truly build a life somewhere else and settle into it comfortably. Your “home” country isn’t really where you grew up – it’s where your life is.

*Other people often do, but that’s a different matter.
**I’m not sure this makes me “foreign,” though. Quite a few of my German friends feel the same way.