Adjusting the capacity of the Fliegl Cargos to 1,000,000 should be possible by modifying the configuration files of the trailer in the game. This change would allow you to transport a significantly higher amount of goods compared to the default capacity.
Regarding wear and dirt adjustment, it sounds like you want to make the trailer more resistant to wear and dirt buildup. This can also be done by tweaking the appropriate parameters in the game files. By reducing the rate at which wear and dirt accumulate on the trailer, you can keep it looking clean and in good condition for longer periods of time.
Overall, these modifications can enhance your gameplay experience by giving you more carrying capacity and a visually appealing trailer that stays cleaner for extended periods. Remember to make backups of your game files before making any changes and ensure that you are comfortable with modifying game files before proceeding.