Is it possible to add/replace texture slots editing shaders or they are somewhat hardcoded in the engine?

I can add samplers to a shader , but i cannot assign material texture slots to them ( i need to specify the asset manually).

I just want to replace the built in slots ( normal , specular , detail and so on ) with slots named accordingly with what they do in the custom shader.

The supported texture slots are hard-coded in the engine. You can search for the enumeration named EEfResTextures. Also look at the datastructure which contains all of the actual material setting: SInputShaderResources and the datastructure that it is converted into for rendering: CShaderResources.

There are generic parameters in these classes but they can only represent floats and vectors, no textures.