A safer and more generally successful approach is to overhaul the graphics. This leaves an opening for a modder to re- introduce an access point and enjoy the missing content. Unless space is a big issue, the programmers usually leave all this content Dummied Out in the game's code. However, some types of mods are discouraged, or even cracked down on, for good reason: a mod in the hands of a player but not their opponent usually means an unfair advantage. They can be unofficial Expansion Packs (new maps or new equipment in the same game), completely unrelated games that merely use the source game's software as a backbone (.
Just because the game designers made a good game doesn't mean you can't make it even better.
