In Basecamp 3.2.1 it is (as far I can see) impossible to edit the name of a route-viapoint. It has the name of the map-item and is always locked.
It can be done after exporting to a gpx-file and editing there (look for the words "<name>xxxx</name>).
It would also be nice to enter prefix for points and a suffix (numbers?)
Can you built it in the next version please?