Epicor Customization - Base Layer

Hi -
I am looking to know that if there is any way to enhance the base customization of Epicor directly.
We know that SDK is capable of Developing a New Base Layer, But Does this capable to modify the Existing Base Layer also ?
I am just looking for constraints in this area …

What do you need to modify? A customization is built on top of a Base layer

No - I am not looking for specific ,
I am just finding out If there is any way of modification of Base Layer (anything in it)

The SDK is what you need for that and it becomes a Base Extension

Thanks Josec - This helps my query !