We never write. Ever.
Every command comes from a whitelist: reads, plus the few mode changes some platforms need before they will show their configuration, each one named, and none of them changes a line of your configuration. You get that list, vendor by vendor, before we start, and your AAA logs can check every command against it. The test that enforces it walks the module instead of a hand-written list, so a command added later is checked whether or not anyone remembered.