Let's imagine creating a mod to replace Judy's mesh with a new model. If the mesh
base/characters/judy/h_judy01.mesh exists within the base game, we can create a custom archive with a new mesh by naming the replacement file identically and replicating the original path.
Now let's say we want our replacement model to use a new texture that does not exist within the base game. We can achieve this by packing a texture (xbm file) within the same archive file. However this new texture must be linked within the replacement model. New files will have no effect of their own unless they are linked by an existing asset.