Add the version in the log_filename itself.
Below is the test case.
naveed=# show log_filename ;
log_filename
--------------------------------
postgresql-%Y-%m-%d_%H%M%S.log
(1 row)
naveed=# select pg_reload_conf();
pg_reload_conf
----------------
t
(1 row)
naveed=# show log_filename ;
log_filename
------------------------------------
postgresql-9.5-%Y-%m-%d_%H%M%S.log
(1 row)
test=# \q
[postgres@localhost ~]$
[postgres@localhost ~]$ ls -lrth /usr/local/pgsql/data/pg_log | tail -2
-rw-------. 1 postgres postgres 3.3K Jul 18 01:25 postgresql-2017-07-18_000000.log
-rw-------. 1 postgres postgres 4.1K Jul 18 01:27 postgresql-9.5-2017-07-18_012530.log
[postgres@localhost ~]$