The level mod out there doesn't give you level 13. It allows you take a second class after level 12 and start at level 1. This would be PERFECT and EASY for Larian to implement. However this suggestion isn't getting noticed by Larian. They would make 25% of their customers EXTREMELY happy and the other 75% wouldn't even care.

It's a win-win-win scenario that and is the only shortcoming the game has.

People aren't asking for level 13+. They are asking for Larian to remove the glass ceiling!