Do you find your system variables change often? Do you have to set it back to default regularly? Why not set them by default in acaddoc.lsp? Read how you can set system variables in acaddoc.lsp. And see some common variables listed here.
You can use acaddoc.lsp to execute commands when open/create file. Load LISP, define new command, update drawings, etc. Learn how to change how AutoCAD command works!