Is it possible to change the voltage of the I2C bus on the Yun?

By default the yun I2C bus operates at 5v. I have confirmed this with a scope.
Most devices I want to connect to operate at 3.3v.
Im curious if it is possible to change the I2C bus to operate at 3.3v.
Looking at the Schematic I’m interested in the part that says JP3 (3.3V/5V)

Does anyone know what this jumper (JP3) does exactly and how to set/unset it?

If not I will have to use a bi-directional level shifter i suppose.

Answer is No.

AVR/Arduino side is 5.0 V
AR9331 side is 2.5V

You need not only Bi-directional but also design for I²C-bus level shifter.