[Q] Disabling flashing / re-flashing

Hi, I’m new to Android. I would like to prevent the reflashing of my device’s entire ROM, even with a manufacturer’s signed ROM (OTA updates are OK). As far as I know, the only way of reflashing the ROM on a non-root, bootloader-locked device is by rebooting into bootloader mode, connecting to a PC and running fastboot commands. Is this correct? Is there any way of disabling bootloader mode? Some devices have a setting Power > Fastboot. Does this do this? If so, is there something I can chmod (by rooting and unrooting) to prevent the user from changing this? Do the reflashing programs, such as ODIN, use the fastboot interface, or is there another flashing interface?

There seems to be a lack of extensive, well-written documentation on anything related to Android hacking so I would be most grateful for a clear, detailed and technical answer.

Many thanks in advance