What do you mean by "system"? Is there an existing transformer that is Delta-Wye, and are you contemplating replacing it with a Wye-Wye (or perhaps reconfiguring its internal wiring to make it a Wye-Wye)? Also, what "voltage regulator" are you talking about? I don't know of any device that regulates the voltage of a transformer, other than an automatic tap changer. If you are talking about regulation, then it sounds like you are dealing with generators. But you don't use terms like "Delta-Wye" in connection with generators.
Can you describe your "system" a bit more clearly?