Debug + Modify PHP Game Script

Possess a GNU/GPL licensed business simulation game which I need modified to meet my specific needs. The following are the desired modifications: (a) Add a password protected administrative interface to allow the administrator to add and remove players, (b) admin interface should allow the administrator to control the playing 'rounds,' and (c) the admin interface should allow the admin to add and remove 'scenarios' or environment and select a different scenario for each game.