No. I don't think anyone knows the trick. I even paid DVDexploder to have a look through their rather impressive lists, but no luck there. So, don't repeat my mistake. I will be sure to post it if I ever get the code.
After several trials, it worked for my Philips PET741/37:
1. Power ON the DVD player without a DISC inside 2. Press the skip keys in this order (the keys are under the "disc menu" and "stop"): right, left, right, left, right, right, left (YOU DON'T HAVE TO GO TO SETUP MENU, just do this in the "blue screen". 3. It will show a menu with region, now use the arrow keys to select "region" and change to "test 0" (all regions). 4. Press OK to confirm. Enjoy
I tried the procedure from Silmara several times and it only worked from the Preferences Menu (Setup and then Preferences Tab and then press the sequence).