I doubt there's any stigma at all in replacing a lead in a long-running show. Wicked, Les Mis, and Phantom have all given huge career boosts to replacements. And, as someone who has seen a bunch of actors interpret Phantom, I can honestly say that their interpretations all differed greatly from each others'.
I'm showing my age here, but I wonder how many people remember that the late Zero Mostel originated Tevye, as opposed to the late Herschel Bernardi, who made the role his own.
If someone gets unlucky, he or she follows a magnetic personality like Rex Harrison. Say "Henry Higgins," and people automatically think of Rex Harrison. I doubt too many folks think of his replacement, Edward Mulhare. Or, God forbid, the actor my parents saw as Higgins in summer stock: Richard Chamberlain.
Yet as many people probably think of Sierra Boggess as Christine as think of Sarah Brightman.
You alone can make my song take flight.
