Richard Roundtree portraying 'Uncle Shaft' in the mediocre Shaft sequel starring Sam Jackson....
But as you say, that was a sequel, intended to be in the same continuity.
How about Bud Collyer and Joan Alexander playing Superman and Lois Lane in multiple series: on the radio, in the Fleischer cartoon shorts, and in the '66 Filmation TV series?
And get this: Olan Soule and Casey Kasem first played Batman and Robin for Filmation in '68 or so, contemporaneously with Adam West and Burt Ward playing those roles in live action. But in the '70s, Soule and Kasem moved over to Hanna-Barbera to play Batman and Robin in
Superfriends (and
The New Scooby-Doo Movies) -- and meanwhile, West and Ward reprised Batman and Robin in Filmation's
New Adventures of Batman. And then, in
Super Powers Team: Galactic Guardians, the final incarnation of
Superfriends, Adam West played Batman alongside Casey Kasem as Robin! Holy mix and match, Batman!
Then there's the
Ghost in the Shell movies having the same voice cast as the
GitS: Stand Alone Complex TV series despite being two separate continuities (at least in Japanese; in the English dubs, only the second feature film has the same voice cast as the TV series, though I think Richard Epcar is Batou in all versions).
Here's a case I'm unsure of: Harry Morgan reprising Bill Gannon in the comedy
Dragnet movie from the '80s. The movie purported to be an in-continuity sequel to the TV series, but given that it was a comedy/parody, it's hard to say whether it should really count as such.
Then there's Leslie Nielsen as Frank Drebin in
Police Squad! and the
Naked Gun movies. The movies aren't really in the same continuity as the show; indeed, the first movie's script consisted largely of recycled gags from the show, so it's kind of a semi-remake. Also, their styles are different.
Police Squad!, like
Airplane!, was set in a universe where absurd things happened all the time and were taken in stride, and Drebin was a deadpan character who was serious by the standards of a lunatic reality. But the
Naked Gun Drebin was a klutzy buffoon whose absurd behavior was looked on with scorn by the more normal people around him. So the character and the world were pretty much rebooted from the series to the movie. (Most of the other roles were recast.)