I'm 1000% on board with replacing oid constants with symbolic names that get substituted programmatically.
However I wonder why we're bothering inventing a new syntax that doesn't actually do much more than present static tabular data. If things like magic proname->prosrc behaviour are not valuable then we're not getting much out of this perl-friendly syntax that a simpler more standard format wouldn't get us. So just as a straw man proposal.... What if we just replaced the data file with a csv file that could be maintained in a spreadsheet. It could easily be parsed by perl and we could even have perl scripts that load the records into memory and modify them. You could even imagine writing a postgres script that loaded the csv file into a temporary table, did complex SQL updates or other DML, then wrote it back out to a csv file.
