Well for one, '010203' isn't a valid regular expression pattern, and two, we need a little more information.
Is the value always going to be '010203' before you change it? If so, a simple [man]str_replace/man should do the trick.
If not, how much of that href is unique? You could do a preg_replace() with a pattern of /(?<=\?sid=)["]+/ although that would affect any string that maches sid?=(something)" throughout the data.
