I can't speak directly for anyone, but my hunch would definitely be no, b/c there are times when the switch is instantaneous. For example, near the end of Act I, when Ruth says "they brought her to my door already in labor..." and then she almost immediately becomes Young Ruth, "but I had no time to think, this baby's comin'" ... There are moments where getting both or all four women on the stage in that amount of timne would be impossible. The book would have to be substantially altered. In the show, all the transformations are seen just through body lanuguage and vocal changes. I believe that everyone involved (Lynn, Stephen, Graci) all believe in the "less is more" approach.
BTW, the above moment is one of my favorites in the show, b/c the change Rachel did was so extrordinary, in that split second, it was as if you saw Young Ruth re-enter her body or something. SO cool.
I think, also the idea that it is a really meaty part for two actresses, a chance for them to really show range, as both Rachel and LaChanze did admirably.
Ask away if you have other questions
Ronni
The Ahrens & Flaherty website