This is more of a “what if” type question than anything as it wouldn’t serve a useful purpose (that I can think of anyways). I recently tried to use some of the OpenMS modules to see if I could create a workflow that ran forever without doing any useful work. It seems that there might not be a way to do this though, as any time I tried to reconnect the output of the last node back to something earlier in the workflow it wouldn’t allow it.
Is this something that is specifically designed into KNIME?
FWIW, I was using the file conversion node in OpenMS, which can easily do file conversions like mzML -> mzXML -> mzData -> mzML (or any other direction of those four formats).