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I want to create custom files with user session information
without .CSS, .JS, header, footer
because I use another admin template

You may then disable Include common files for your Custom File.

if you use Include common files you can't call Auto-Update Value

1. For CSS (only), you may enable the advanced setting Disable project CSS styles,
2. To customize js, you need to customize the layout.php, see Customizing Template.
3. You may also write an extension to change the layout.php, see Making Extensions.