Log file location

Is it possible to change <LOG FILE> in a session such that its valid only for that session?

No, at least not straight forwardly for me.

Command:
set session log_directory to '/home/thiemo/tmp';

Error:
FEHLER:  Parameter „log_directory“ kann jetzt nicht geändert werden

I do not know what that's supposed to mean? A reload of the configuration did not make a difference. Maybe that it is not possible to change it by the set command.

For my purpuses this is not important as long as the parameter log_min_messages is not verbose. Debug and such message will not land in the sever log. Nonetheless, I do not feel totally at ease with this.