PHL Controller described a confused routing event when attempting to change an ICAO flight plan from a RNAV departure to a conventional procedure; the reporter indicating more training is needed for clarity.

Narrative

We had another aircraft that; after his flight plan was filed; needed to depart non-RNAV. Again; although we knew what the non-RNAV routing should have been; we were unable to remove the PDR with the RNAV routing. After amendment (revision 3); his route showed +..OOD..TEBEE..HAYDO..SBY.+ .+OOD.OOD198..SBY018.SBY.V1.CCV... At that point; his equipment suffix had been changed to /A; but still the PDR appeared. The full readout of his ICAO flight plan information after the 3rd amendment showed as follows: ...FLR I FLT S WAK M EQP DOV SRV C ALA KIAD OTH...RNA 1 RND 1 RNE 2. Because we were unable to remove the RNAV PDR; Tower had to advise the Departure Sector; who then had to advise the Center Sector. Minor problem; and since the non-RNAV underlays the RNAV route; a lack of this communication occurring would not be problematic. Still; the fix should be able to occur while the aircraft is on the ground; not be reliant on Local and Departure remembering to coordinate with the next sectors. I do not know who can answer the basic question: how do I change an ICAO flight plan from RNAV to non-RNAV? I suspect that the 'RNA 1 RND 1 RNE 2' has to be removed somehow; since that has to be there regardless of what's under EQP if you want to get the RNAV routing; but no one knows how to do it. My recommendation is exactly the same: a manual. Some better-informed support personnel would be nice too; but I'm happy to learn on my own since that seems unlikely.