Animorphs essentially did this with most of the cover models, as the original models grew up and went off to college. The re-release, of course, did it again, replacing the original covers with updated ones and cover models who are the right age at the time of re-release.
Steve O'Brien illustrated the first four Dave Barry books. The rest of the books that had illustrations (barring Dave Barry Slept Here and Dave Barry's Only Travel Guide You'll Ever Need, which only had maps) had Jeff MacNelly, and then Gary Brookins after Jeff's death. (Brookins also succeeded Jeff on his two comic strips, Shoe and Pluggers.)
An in-Universe example occurs in The California Voodoo Game, when the role of Bobo the guide is commandeered by Alex Griffin so he can keep an eye on Bishop. The players take the exchange in stride, assuming that Bobo's original Game-actor came down with the flu or something.