Timestamp Format

how can I make a timestamp data type be outputted without the time zone?

I expect:
"YYYY-MM-DD HH:MM:SS"
instead of postgresql output:
"YYYY-MM-DD HH:MM:SS-timezone"

I know I can do that by using some functions on the select query, but my
idea is to get this result without altering the queries, like changing an
enviroment variable or a setting in the configuration file or whatever like
that, but NOT in the query.

from what I've read so far, set DATETYLE won't help at all, it just changes
the way the date and the timezone is printed, but it won't  ouput a strict
'YYYY-MM-DD HH:MM:SS'

can postgresql do this at all (once again, without using functions or
altering the query)

Thanks in advance, Alex