A bit different, as already discussed there's a good reason for modern day incarnations of Eric and Charles to be associated with the Civil Rights movement. Whereas the potential Superman change just seemed pointless.
Also altering the colour of supporting characters is different to doing the same with our main characters. There's plenty of black/coloured comic book characters out there who we also wouldn't want recast as White.
I'll partially buy your Civil Rights Movement angle, because as I said previously, would be a good idea to update Mag's Holocaust survivor background due to the age limits that puts on the actor casting.
But we both know that if we get a Mulatto Prof and Black Magneto, there will be resounding "Woke!!! Reeee!!!!" to be heard, no matter how sensible the backstory changes are.
Would we call film Magneto a supporting character still? He tends to kind of take the spotlight as he's one of the most interesting characters, McKellen and Fastbender both did it.
Not entirely related, but I just remembered how we had Ra's al Ghul who's normally Middle East and Bane who's normally Latino (iirc) be whitewashed in the Nolan films, and hardly saw anyone point it out back when first got said films. lol
We seem to be mostly past the point of stuff like that happening now, at least.