I've listed here which codes I can do 
Ceiling Colors
Get rid of the end screen
Floor Colors
Changing the PacMan to Sprites
Change things in the menu ( Menu color,names, etc etc.. )
Change Skill Names
Change Exit messages, etc..
and maybe more :-)
That was basic! Now comes Advanced..
Advanced:
Change the Open/close speed of the doors.
Deleteing the Boss Dead Animation Delay
And the codes by myself:
Add more smoke to the rockets from bosses..
And some others which I dont know which catogory ( basic or advanced ):
In game messages ( dont understand 100 % because by ammo etc he gives an error, only a medkit works I saw )