Cannot change archive_command with a reload

Hi all;

we have a cluster running with an archive command that is failing.
I tried a reload and the value does not change

Tried a set_config and I get this error:

select set_config ('archive_command', 'cp %p /data/wal_tmp/%f && mv
/data/wal_tmp/%f /data/wal/&f', 'false');
ERROR:  parameter "archive_command" cannot be changed now


Thoughts?

Thanks in advance