I renamed the file to backup-init.tcl but it didn't help, or at least there's no notice from this script when the server starts up. Here's a snippet from error log from the time of server restart. As far as I understand, server does sourcing directed in 0-acs-init.tcl and then jumps to load packages but does never source the backup file.
I have no problems sourcing -init.tcl scripts in the tcl directory. See https://openacs.org/forums/message-view?message_id=66742 for an example. While it doesn't have any ns_log statements, you can easily verify that the script was sourced by visiting the filters page of the monitoring package.