You cannot change the digital logic output level to different than the default for your USB hardware. As an alternative to changing the digital output levels in the USB-6363 itself, you could build or buy required electronics components to change the logic levels. These devices are often called "Logic Level Converters", "Level Shifters" or "Level Translators". However, National Instruments does not produce these devices.
Another option to control the voltage output more accurately would be to use analog output. Below is a short example showing how to convert digital logic to analog. Instead of sending Boolean value to Digital I/O line, you can convert boolean data type to numeric (FALSE - 0, TRUE - 1) and then multiply by the desired value for voltage high level.
This way you can represent your digital data as analog signal and use analog outputs of your I/O device. However, make sure you set the high level within the device specifications