1. After reload you get have settings from config (default)
2. you must use false as 3 parameter - it is is_local - just for current 
transaction

    sqldb=# select current_setting('log_min_duration_statement');
     current_setting 
    -----------------
     -1
    (1 row)
    
    sqldb=# select set_config('log_min_duration_statement', '1000', false);
     set_config 
    ------------
     1s
    (1 row)
    
    sqldb=# select current_setting('log_min_duration_statement');
     current_setting 
    -----------------
     1s
    (1 row)