Well, I would want to answer this question by looking at the way that Blanche tries to pursue and gain Mitch, even though he is not her ideal man. Let us remember that Blanche's flight from reality causes her to try to present herself as a Southern belle, a lady who excites and attracts the attention of men. Except with Blanche, we can go even further than this, and say that Blanche's existence depends on sexual admiration from men to shore up her faltering self-esteem. Marriage to her is her only escape from her past as a fallen woman and the many secrets that she hides. For Blanche, a woman who is increasingly running out of options, Mitch is her only hope, even though he is not the chivalric gentleman that she hopes for. Thus we could argue that Blanche, in settling for second best by pursuing Mitch, is definitely adjusting her personality in this sense in her attempt to achieve happiness.
Of course, the tragedy of Blanche's situation is that she is unable to see that happiness will never be hers whilst she is so dependent upon a male figure in her life to try and sort her out and save her. Until she is able to face her reality and who she is, stripped free of pretensions, she will never be happy, and Stanley in particular in this play is the main vehicle who is responsible for completely destroying her character and leaving her a shattered remnant of her former self.
In Tennessee Williams's play A Streetcar Named Desire the character of Blance Dubois is a broken woman who has lost basically everything in her life. She has lost her good reputation due to several sex scandals including some that involve students. She has lost her teaching job, her family's plantation home, and her parents. Now all that she has is her memories and the mercy of her sister, Stella, who lives with a misogynist husband named Stanley.
There is a clear indication that Blanche does desire happiness, despite of it all. The problem is that she continues to act in her ways in order to achieve that happiness when it is clear that it is the way that she acts what gets her in huge trouble in the first place.
She does accommodate her personality, but only to a point. She tries to be charming to Stanley and his friends assuming that they will understand her attempts at creating Southern charm. She also does her best to help her sister cope with her husband and her pregnancy, but only by defying Stanley, which is a capital mistake in the Kowalski household. Furthermore, she tries to play the genteel woman with Michael only because he is her last hope, not really because she loves him.
Concisely, there is a disconnect between Blanche's true desires and her possibilities for them. All this is caused by her inability to change her behavior from passionate and dramatic to calm and sensical. However, in Blanche's world being calm and collected as well as typical and unassuming does not belong in her personality. This is what ultimately causes her happiness to miss her.