The short explanation
HDMI has a dedicated wire called Hot Plug Detect, HPD for short. When a display is connected and powered, it pulls that line high. When it disappears, the line drops. A short drop-and-rise is a hot plug event, and to a source it means: the thing downstream may be different now, read its EDID again.
Where you run into it
Sources cache EDID aggressively, and for good reason — re-reading it constantly would be wasteful. The side effect is that changing an EDID does nothing until a hot plug event tells the source to look. That is why people end up unplugging cables: they are generating an HPD pulse by hand.
It also explains a class of annoying behavior. Turning off a display drops HPD, the source sees the sink vanish, and it rearranges what it outputs. Turning the display back on triggers a fresh handshake, sometimes at a different format.
How the DR HDMI 8K handles it
The DR HDMI 8K has an ISSUE HOTPLUG button in its configuration page: a soft reset of the chain without touching a cable. Selecting a new EDID table fires one automatically. The TX +5V force option (on by default) decides whether the unit detects the display at its output at all; switched off, the unit behaves as if the output cable were unplugged.
Want to test your own HDMI chain?
The DR HDMI 8K is sold through the HDFury.eu web shop.