AFAIK you can create process definitions programmatically. I just don't recall if they're based upon jPDL or PVM. Look it up in the javadocs. Should be there. Regarding creating a process definition file (I am not sure about your question) you should accomplish this on your own by using some XML tool since the jPDL language is XML-based and not to complicated.
And yes, it is possible to maintain different version and use them on the same time. Should be in the userguide.
Thank you very much for the info.