Do you mean when you create a stereotyped association you want the role names to be pre-filled? The only way that I know of would be to write an add-in that implements EA_OnPostNewConnector
"All properties are equal, but some are
more equal than others" (with apologies to Mr Orwell).
Yes, for an arbitrary Arc metatype, you can set all sorts of properties in either the origin or the destination or both, but not the role names... (and, as it happens the arc, name and alias). Now, I'd rarely use them in this way, but I see no reason why they shouldn't be available. To me, it makes just as much semantic sense as specifying the AggregationKind or the Multiplicity.
Paolo