It's worth noting that the single player component of CZ is a separate code base from the multiplayer CS component.
The multiplayer component will simply be the latest version of the counterstrike with exclusive multiplayer maps created for the CZ box.
The single player component is NOT a mod for Half-life, anymore then Sin is a Quake 2 mod.
Condition Zero does not require HL to run, and thus falls out of the mod category. Condition Zero is a completely self sufficient single player package created with the Half-life engine. Those who wish to use CZ to create singleplayer mods and levels will find that Ritual has added a number of excellent features to the code base to allow for more dynamic gameplay and increase customizable art and level assets usage.
So in short if you wish to make multiplayer mods for CZ, you're going to simply be working with the latest and greatest version of CS. Those wishing to create singleplayer content for CZ will have access to the tools and enhancements that ritual has made with the CZ code base.