If so, how? I have 4 wire and 2 wire devices I would like to connect on the same data line. I know you can convert 4 wire to 2 wire easily at the master, but is it possible farther down the line, say after a string of 4 wire devices?
4 wire device provide full duplex communication and 2 wire half duplex communication. It depends what kind of transceivers you are using and what communication you would like to have (half or full duplex).
It is possible to use 4 wire transceiver on a two wire bus. With more information in your question you would get much better answer.