Yeah, I hit that bottom. I have 5 classes, which I do not wish to change, and an idea for 6th/7th/8th class as well. Is there any modification/console command/script code that allows to create more then 5 custom classes?

Also, is there any reason behind limiting it to 5?

Don't think you can... and no idea why it's limited to 5. IMO they should just let you switch weapons/etc during the game.