What are the rulings regarding marriage, hijab, and prayer applicable to a person who has undergone a sex change operation from male to female, and is this person considered expelled from God's mercy despite their commitment to acts of worship?

What you have done, transforming from male to female, is forbidden if your organs are male and your chromosomal makeup is (XY). Inclinations or feelings are not to be considered. The obligation is to repent to Allah and return to your original state if possible, while changing your outward appearance to look like a man. Know that you are male, so it is not permissible for you to mix with women or wear their clothing. If you repent sincerely and do what you can to return to your original state, acceptance and forgiveness are hoped for you.