I am also interested on any updates on historical place names. The ishistoric flag seems sufficient for place names that have changed over time, but is is problematic for other cases -- especially without any ability to add a date.
I am also finding the ishistoric flag to be problematic since some entries seem to require a higher user level to add the flag. (I tried to mark Verdun-sur-Meuse as historic, but was given a "you are not allowed to update this alt name" error.
Also, I am noticing in earlier posts to this thread and the geonames user manual that fr_1793 was an accepted pseudo language code, but it is no longer listed in the pseudo language code list that appears when viewing or editing a record. Has this been removed?
The alternate names table has two brand new columns 'from' and 'to'. They are used to specify the period from-to when the name was used.
I have marked Verdun-sur-Meuse as historic with the to field '1970' and Verdun with from '1970'.
The new columns are exported in the new file alternatenamesV2.
The user level concept helps to protect some features agains undesired updates. We can increase your userlevel.