I am sorry, I do not understand what exactly you want to achieve using Rebex components.
Is your question related to Rebex SSH client or server?
For Rebex SSH client - shell interpreter is related to the server, so you should ask at the server side for help.
For Rebex SSH server - shell interpreter cannot be changed. The server has its own simple shell, which supports only couple of commands (most of them was added just to enable SCP support). You can write your own interpreter, but it would require a lot of work.