Add differences into table

Using this code

     select p.RecNum
     from "Project List" p
     left join Week01 w
     on p.RecNum = w.RecNum
     where w.RecNum is NULL

I get a list of all RecNum that exist in "Project List" but not in "Week01". Is there a way to then add all of those RecNum into Week01.RecNum as well as set Week01.UserName to "JustMe"?