If the second presets has sub-settings in the same categories as the first preset, yes, the second preset wins (overwrites) what the first preset changed. If the second preset's sub-settings do NOT overlap, the first preset's non-overlapping categories will not be overwritten.
This is the power of being about to create multiple presets with only certain sub-settings included so you can mix and match to get to the final combinations.
Note, when importing you can only apply a single preset at the time of import but you can apply additional presets in the Library using Quick Develop.
