Joguwa86,
It's your decision, of course, but I implore you not to take a file to any part of your poor little Mann!!!
If you are having problems with magazine retention, it may very well be due to the gun's having been assembled improperly. The stirrup-shaped spring that is responsible for creating the tension on the magazine catch also serves as the trigger return spring - the bottom part of it fits into a groove on the rear of the mag catch, and then the two side prongs bend sharply in on either side of the catch and go behind the mag catch pin (before the pin is installed, of course!). Then the upper ends of the two prongs have to go in the right spots (one against a cutout in the frame and the other against the trigger, as I recall). You are working in very close quarters, and it is a difficult and tedious process to get everything in the right place. It would be very easy for someone mechanically disinclined or just impatient to do it the wrong way, with the result that the catch's function might be impaired or simply reversed.
So before doing anything else, I would suggest you go to Gerhard Schoenbauer's website, which has exploded views of many pocket pistols, including the Mann (about halfway down), and print out the picture showing all the Mann's parts laid out, and study it until you feel that you have a basic feel for what the various parts do. If you are the type who enjoys such work, go ahead and carefully (using the right screwdriver bits and punches!) disassemble the gun. The Mann is actually quite a simple firearm as you will see.
Here's the link to Gerhard's website:
http://www.vestpockets.bauli.at/archiv/mann1p.jpg
Let us know how you make out!