The Mini-USB to USB cable looks like this
. The Mini-USB connector is the same one that is on one end of the Corsair LINK cable
that came with the H100i (top cable in that photo). You would take out the Corsair LINK cable and plug the Mini-USB to USB cable into the port on your H100i pump/CPU block
and into an external USB header.
Did you end up trying to uninstall the H100i via Device Manager? If not, please try that, it'll be under Device Manager\Human Interface Devices and then it'll be one of the ones that is listed as just "USB Input Device." To figure out which one it is, right-click and go to Properties\Events and look at the list there. It should show something like this:
You'll notice that USB\VID_1B1... is the same path you modified in regedit. Go back to the main Device Manager windows and click uninstall, then reboot your computer. Then go back to regedit and see if that Device Parameters folder is back.
Sorry this hasn't been more fruitful yet!
EDIT: Saw your note about the gadgets - will send you a PM about those.