Is it possible to adjust the tweeter level?

Yes,internally there is a jumper that can be shorten and then the tweeter level decrease whith -2dB.You need to open the cabinet by dismantle the driver to make it possible.

One of my drivers are broken and I don't want to send the whole speaker. Am I allowed to change it by myself?

Yes, after you've consulted with us, we can instruct how to change the driver.