In Plant 3D there are two files for each spec, a PSPX and a PSPC. What are they for?
The .PSPX file is a ZIP file containing header information for the spec and the branch table. This file is the one referenced by the Spec Editor. It may be opened and the contents modified using a suitable text editor.
The .PSPC file actually contains the definitions of the fittings. It is a SQLite database, the contents may be viewed using a SQLite database browser.