On 2nd of September, Fujii Masao committed patch:
Support ALTER SYSTEM RESET command. This patch allows us to execute ALTER SYSTEM RESET command to remove the configuration entry from postgresql.auto.conf. Vik Fearing, reviewed by Amit Kapila and me.
Continue reading Waiting for 9.5 – Support ALTER SYSTEM RESET command.
On 18th of December, Tatsuo Ishii committed patch:
Add ALTER SYSTEM command to edit the server configuration file. Patch contributed by Amit Kapila. Reviewed by Hari Babu, Masao Fujii, Boszormenyi Zoltan, Andres Freund, Greg Smith and others.
On the next day, Fujii Masao committed patch:
Add tab completion for ALTER SYSTEM SET in psql.
Continue reading Waiting for 9.4 – Add ALTER SYSTEM command to edit the server configuration file.
Similar question has been asked many times on mailing lists and on IRC. Sometimes it's not mail sending, but file/directory creation, or something else that generally requires some interaction with “world outside of database".
Can it be done? Sure. How, then?