MomCares, yes, a composer could work on their musical and fine tune it at the Mercer Songwriters Project but that is not the same as "workshopping" a musical which is what the OP was asking about. For instance, my D's musical was workshopped at Yale Institute for Music Theatre where she had a Broadway director and the workshop was cast in NYC with Equity actors and a workshop production was staged to a live audience. At Mercer, one could work and develop a piece but there would be no cast or reading/workshop production of it. Mercer has GREAT value....don't get me wrong! So, does MacDowell Colony (where my D had a fellowship residency)! But it is a different experience than workshopping a musical and so I was just responding to ideas for that itself for the OP.