Explore the transformative power of fooling in Twelfth Night.

Twelfth Night is ultimately centered around Viola's transformation into Cesario, the woman disguised as a man, in order to access Orsino's court. This is where your use of the specific term "transformative" is a particularly apt way of describing it, because really, Viola's transformation of identity (and the complications which follow from that transformation) will drive the plot that follows.
Orsino is pursuing Olivia and sends Viola as his representative, only for Olivia to fall in love with the disguised Viola instead. Meanwhile, Viola is secretly pining after Orsino. Later, Viola's twin brother, Sebastian, will arrive, adding additional complications to the confusion, with Olivia, mistaking him for Cesario, marrying Sebastian, and Viola being mistaken for her twin brother in turn. Across the course of the play, that initial deception (by which Viola disguises herself as a man) takes on a life of its own, as more and more people are drawn into this net of confusion.
That being said, it is worth noting that, for all the confusion her trickery creates, Viola does not have malicious intent. This contrasts the far more mean-spirited deceptions carried out by Toby Belch and Maria, who trick the steward Malvolio into believing that Olivia is in love with him, with the goal of humiliating him.