Transformer designed for K-factors do not have any special property to mitigate harmonics.
Harmonics can be controlled by use of proper configuration :
Delta -- star
Delta -- Zigzag-Star
Dual transformer with 30° phase shift
K-factor does not indicate its capacity to mitigate harmonics. K-factor is an indication of
composition of percentage harmonics as seen in tables, where-as K-rating is the
capacity to transformer to handle harmonic loads of that K-factor :