Does replugging a Thunderbolt display necessitate a system restart? Is there any danger in hot-plugging and un-plugging an external (Apple) Thunderbolt monitor (from USB-C), or is it safer to shutdown the computer first?
Is there any danger in hot-plugging and un-plugging an external (Apple) Thunderbolt monitor (from USB-C)?


It is absolutely normal to hot-plug/unplug an external display connected over Thunderbolt or USB-C port of your Mac.

It is not required to shutdown your Mac just to plug/unplug an external display.