A preset can either change a setting to a specific value or leave it as it is.
A quick and easy way to have the preset not touch the white balance is the following:
- Apply the preset to an image.
- Right click the preset's name in the Presets pane and choose 'Update with Current Settings'. In the dialogue that pops up, untick 'White Balance'. Close the Dialogue with 'Update'.
Alternatively, if you want a new preset (instead of changing the existing one), at step 2, instead of 'Update with Current Settings', hit the plus button in the upper right of the Presets pane and create a new preset from there. The same dialogue will pop up.