The AutoCAD Electrical toolset symbol libraries are installed in \Users\Public\Documents\Autodesk\Acade {version}\libs\{library}\.
The default {library} folder depends on installation choices, for example JIC or IEC. You can modify the ".dwg" version of each symbol to comply with your specific standards or client requirements.
Tips and Hints
Leave all symbol attribute definitions and geometry on layer "0" and that entity color assignments are by layer. Let AutoCAD Electrical toolset manage what layers the various parts and pieces of your symbol get put on at insertion time. This layer naming scheme is set up in the Define Layers dialog box. If you want certain layer naming maintained on your inserted components, select Apply to entities on layer "0" only. With it checked, non-layer "0" entities maintain their existing layer names as the component inserts into the drawing.