I do not have first hand experience with this; so I can't directly answer your question. But, this mod should not change the tone, or timbre, of your bass. The only noticeable difference should be more flexibility in the use of your two volume controls.
However, with the mod in place, and being able to adjust the relative output of the two pickups via the internal gain controls, then you will be able to adjust the height of each pickup to change it's tonal characteristics as you wish; whereas without the mod, the effect on volume of changing the pickups heights might have been too constraining.