Yes it can be done. At the risk of doing your homework assignment…in the simplest sense, if you reverse individual ‘coil’ connections on the (high or) low side, you can produce 60° lead or lag from primary to secondary. Without giving an itemized list of changes, draw a Y on paper. Draw lines 180° opposite of each leg, symmetrical about the neutral. This results in an “asterisk” figure that can be connected to produce a 180°, 60°, or 300° phase shift. See ANSI/IEEE C57.12.70-1978 §8.5.
Now report back to the group on the Hoepner connection.
As busbar says, you can do it at your own risk. Such a connection group is uncoded.
In practice you can get two possible combinatios: Yy2 or Yy10. Both require the inversion of one side (preferably low voltage side, as hight voltage side could face some dielectric problems). For detaled connetions, let's assume that A, B, C and a, b, c, are HV and LV windings in positive sequence for original transformer Yy0, and A*, B*, C* and a*, b*, c* the new transformer windings. Then:
For Yy2 connection group:
A*=A; B*=B; C*=C; a*=-c; b*=-a; c*=-b
And for Yy10 connection group:
A*=A; B*=B; C*=C; a*=-b; b*=-c; c*=-a
