...states that this revised Prologue was spoken on the tenth night, by which I guess Sheridan felt safe in presenting it!

The footnotes also indicate that "this form" in the 7th line of the Prologue refers to "the figure of Comedy depicted on one side of the stage" and "their favourite" in the lines you quotes refers to "the figure of Tragedy depicted on the other side of the stage".

So obviously the speaker of the Prologue would gesture appropriately.

As for what those last 4 lines mean, they are very cryptic to me as well, even with those footnotes. It seems as if Sheridan is suggesting that this play has elements of Comedy AND Tragedy, but beyond that, I can't see why the tragic aspect would be subject to oppression, and why it would hate guilt.