Hi Nachladen, welcome aboard.
More 'slots' in the basic.cfg don't show up on the crew screen. You would have to change the graphics for additional slots and add bindings and functionality to your new slots.
Are you a member of the development team?
If you only want to have more slots for recreation - use the repair compartment.
Change the data accordingly to the bow and stern quarters.
I did it in 2005, before there was a 'SH3 Commander no fatigue option' Steve already mentioned for you.
You can 'move' gun positions, but as far as I know, you can't add extra gun positions. You can change guns - like sporting a 3.7 cm FLAK on a Type II.