There are three things that the mod maker may have done.
He may have added a texture set and assigned it to a new object in the geck and placed those new objects where the originals were. If that's is the case, then you would have to hightlight each locker in the Geck and hit 'Cntl F' then select the object you want to replace the ones in the mod with.
He may have used overrides - meaning he has custom meshes and textures in the coresponding folders that replace the originals. In this case simply deleteing the custom meshes would force the game to locate them in the BSA files and render them in the original form.
He may have modified the original meshes (.nif iles) and pointed their BSShaderTextureSet to the new textures. In this case you can do the same thing as the above solution, namely, delete the custom meshes.
He may also have done paertial combinations of the above.
All of this is at least intermediate Geck modding and shouldn't be done unless you know what you are doing.
What is the name of the mod?