If the secondary had 100 turns a 2% tap of 102 turns would decrease the secondary voltage by about 2%, whereas a 2% tap of 98 turns would increase the voltage by about 2%.
Adding 2 turns to the secondary winding will
increase the output voltage, assuming that everything on the primary side stays the same. The secondary voltage would be reduced if extra turns were added to the primary winding (and the primary supply voltage stayed the same).