Have there been instances of a white character having their race/ethnicity changed to anything other than black?
Richard Dragon was portrayed as Chinese in the recent animated movie but that was actually his ethnicity in Denny O’Neil’s original novel, so it was kind of just bringing the character back to his roots.
The original version of Karate Kid from the LSH. He was drawn to look Caucasian when introduced in the 60's, even though he was supposedly biracial (Asian father, Caucasian mother). In the early to mid-70's, around the time DC gave him his short-lived own book to cash in on the martial arts craze, artists started drawing him to appear decidedly more Asian in appearance (Mike Grell specifically drew him based on Bruce Lee's appearance). By the end of the 70's, after his title was canceled, and into the mid-80's when he was killed off in the LSH's Baxter-paper book, he was back to being drawn to look Caucasian again.
Lana Lang was played by Kristin Kreuk who is half-Chinese on Smallville, and by Emmanuelle Chriqui who is Moroccan Jewish on Superman & Lois. Maggie Sawyer was Latina in the Arrowverse. There's the Latina Supergirl and the Riz Ahmed-based Constantine they're apparently looking for. Noah Centineo who'll play Atom Smasher is of mixed Puerto Rican descent and I guess Mercy Graves also counts since she's been anything from white to black to Asian to mixed-race Indian.