Ick. Why suggest copying the entire DoomPlayer definition? Just have the new player class inherit from DoomPlayer.
Note that you'll have to redefine the two Player.StartItem definitions from DoomPlayer as well, since adding a new one will toss the old list (for ease of inheritance). Just be sure to explicitly give a chainsaw, the fist, a pistol, and 50 bullets. FYI, the first-defined weapon is the one that's selected at first.