If I already e-filed 1120-S, can I create and file a superseding return before 4/15 deadline?

It depends. If you are filing a corrected Form 1120S after the original filing deadline of March 15, the form is considered "amended" and not superseded. However, if you filed a request for an extension of time to file, you have until October 15 to file a superseded return.

You can prepare a superseded or amended return in TurboTax Business. However, the return will need to be printed and filed by mail. At this time, TurboTax does not support e-filing more than one return. As mentioned above, you will need to write "Superseded" at the top of all forms before you mail them. TurboTax will mark an amended return as such (no need to write anything on the forms).