How to edit `postgresql.conf` with pgAdmin 4?
Workaround: ALTER SYSTEM

As a partial workaround, Postgres 9.4 added a feature to dynamically set the properties seen in postgresql.conf: ALTER SYSTEM commands.

ALTER SYSTEM SET configuration_parameter { TO | = } { value | 'value' | DEFAULT }

ALTER SYSTEM RESET configuration_parameter
ALTER SYSTEM RESET ALL  -- Clears all the settings set via `ALTER SYSTEM SET`. 


This provides a convenient alternative to manually editing the postgresql.conf file.

Example:

ALTER SYSTEM SET wal_level = replica;


How does it work? 


A postgresql.auto.conf file is written by the ALTER SYSTEM SET command. 
This file and postgresql.conf are both read, so you can combine these approaches if desired. The auto file trumps the hand-edited file for coinciding properties. 
For reliability, a postgresql.auto.conf.temp file is created to rollback to the original state in case of error.


Caveats:


Settings do not take effect immediately. Read the doc.
Must be superuser to execute.
Cannot be called in a transaction block or function. 
Cannot set data_directory.
Obviously misuse can be dangerous to your database system, so be careful.


Tip: To read the value of the settings, see this Question, Query for all the Postgres configuration parameters‘ current values?

Workaround: Use command-line editor as postgres user

You can run a simple text-editor like nano from the command-line run with the privileges of the postgres user. Open the pg_hba.conf file, edit, and save.

For example, on a Unix/POSIX-oriented OS such as BSD or macOS:

sudo -u postgres nano /Library/PostgreSQL/11/data/pg_hba.conf


For more info, see the Question, Switch user to 'postgres' user on macOS results in “su: Sorry” error