Is changing a supplication for marriage to a specific person, after receiving glad tidings about him in a dream, to a supplication for marriage to another person who is better than him, considered an act of having good expectations of Allah or an act of displeasure?

There is no harm in a woman supplicating to her Lord to marry her to a specific person, even if she supplicates for one person and then for another. The advice is that she should ask Allah to facilitate goodness wherever it may be, and to grant her what is beneficial for her religion and her worldly life, and to entrust her affair to Him, Glory be to Him; for His choice for her is better than her choice for herself.