Well, I guess there was something wrong with the old file. I saved Bart's file (where I had copied my function and its call) under another name and then deleted the extra stuff from both files.
After that, my situation was just about the same than before the tricks, i.e. two different init files. The only difference was that I this time named the backup file acs-pgbackup-init.tcl. Now everything works just fine!
