No reason was announced for the cast change.
Actress-comic Kathy Najimy will direct the production, which will run through May 17 at the L.A. venue. Opening night is scheduled for April 19.
The cast will also boast "American Idol" finalist and former Hairspray star Diana DeGarmo, West End musical actor and "American Idol" contestant Tom Lowe, and musical and film actress Tressa Thomas.
Susan Mosher has been seen on Broadway in Hairspray and Off-Broadway in Suds. She was in the original Off-Broadway company of Back to Bacharach and David, and her screen credits include "Without a Trace," "If These Walls Could Talk 2," "Veronica's Closet," "The L Word" and "A View from the Top."
Javier Velasco will choreograph the production with musical arrangements by Steve Gunderson. Back to Bacharach and David — described as "a night of amazing voices, comedy, and a tribute to the brilliant songs that Burt Bacharach and Hal David wrote from 1960 to 1970" — was conceived by Najimy and Gunderson.
In a statement director Najimy said, "These songs defined 'cool' then and define 'cool' now. Every generation since this music was created, has found relevance in it, been drawn to it, and recreated it. This show is a blast to work on — sexy, moving and funny — with brilliant arrangements. . . . We approach the Bacharach-David catalogue with tons of humor and awe, updated with a modern twist — with four of the most kick ass voices around — and we are thrilled to have the encouragement of Mr. Bacharach and Mr. David themselves for our new production."
Composer Bacharach added, "I saw this show in San Diego a couple of years ago and was quite impressed with the presentation and the musicality. I have always been very particular about how my music is presented on stage and have had some disappointments in the past. Steve Gunderson's musicality and Kathy Najimy's direction makes this a very exciting prospect for me."
The design team comprises set designer Myung Hee Cho, Tony Award-winning costume designer Gregg Barnes, Ovation-winning sound designer Martin Carrillo and theatre and rock concert lighting designer Anne Militello.
The Music Box @ Fonda is located at 6126 Hollywood Blvd. For tickets visit www.etix.com.