Yes. You can change your name whenever you want to. You can be married and not have the same last name. Me and my husband got married almost 4 years ago, i havent changed my name yet...( im going to but have to get some documents from the state we got married in, i just havent done it yet)
If you are married but separated you can change your last name legally without divorcing. You will be charged a fee for the service. You should consult a family lawyer for legal information about changing your last name.