Halfway through previews of his rousing, dance-filled musical, “Fela!” which opens September 4 for a two-and-a-half-week run, the choreographer Bill T. Jones, 56, was still fine-tuning sequences every afternoon. He has won every possible accolade as a choreographer in concert dance and a Tony Award for his work in the hit Broadway musical, “Spring Awakening.” But “Fela!,” which is based on the life of the great Nigerian musician and political activist Fela Anikulapo Kuti, who died in 1997 at age 58, marks the first time Mr. Jones has conceived, directed, and choreographed a musical theater production.