One of the great privileges of steady theatergoing is that you get to keep falling in love again. You’ll cautiously revisit a show you once lost your heart to, thinking it can’t possibly be as intoxicating as it was the first time around, especially if there have been cast changes.

But then you discover that lightning really can strike twice — or thrice, or more — in the same place. And you wake up the next day, happy and lightheaded, thinking you just might rejoin the ticket queue that afternoon.

Such was my illuminating experience recently on two successive nights, with established revivals of musicals that have introduced new actresses in pivotal roles. In the Tony-winning Lincoln Center Theater production of “The King and I,” Marin Mazzie has taken over the pronominal role of the “I,” Mrs. Anna Leonowens (with a new King in Daniel Dae Kim), while Heather Headley is now inhabiting the sinuous skin of the honky-tonk diva Shug Avery in “The Color Purple,” a Tony front-runner this year.

Both women have the unenviable task of replacing shimmering stars of box office weight. Ms. Mazzie succeeds Kelli O’Hara, whose Anna won her the Tony last year; Ms. Headley has taken the place of Jennifer Hudson, an Oscar-winning pop singer and a household name.