Tristan Thompson is all about changes these days ... and he's just changed his citizenship to the U.S. of A.
Tristan was sworn in as an American citizen earlier this week ... shortly after deciding to join the Boston Celtics.
Tristan was a Canadian citizen and came to the United States to study at the Univ. of Texas back in 2009. He was only there a year, before joining the NBA draft. Tristan played for the Cavs for 9 seasons, beginning in 2011.
Tristan says, “I came to the U.