One measure of an actress is her ability to melt into different roles with credibility and impact, and Alison Hernan accomplished that splendidly in two productions at Cleveland Public Theatre. Last fall, Hernan played the politically tormented Zillah, a desperate woman who constantly scribbled hate letters to President Bush, in Tony Kushner's A Bright Room Called Day. Hernan's character exuded frustrated angst from every pore, even believing that she could bring down the government by shaking hands with individuals in the administration, hoping that in some way her anger might work its way into their bloodstream. And then, in a remarkable change of pace, Hernan crafted a despotic but slyly sexual vixen, dressed in libidinous fetish outfits, as the lesbian boss Ms. Curtis in The Secretaries. From hardball politics to soft porn - that's flexibility for you.