i'm not sure i understand your question. are you saying you have an existing password that you want to keep, AND want passwordmaker to auto-populate for you? if this is the case, yes it can be done, and the info you seek is in the
FAQ. see the 7th item:
"I want PasswordMaker to automatically populate webpage forms for me, but I don't want to change my password on some sites. Is PasswordMaker still a good choice?" for full details. if i misunderstood your question, please restate.