Please re-read the warning.
It's the INK CARTRIDGE cover SWITCH. You don't want to pull a cartridge when the printer thinks the ink cartridge cover is down.
This can ruin the contact.
However, when a cartridge resets, the printer will stop and show a cartridge error. Just pull the small ink cover key (black plastic thing you got with the CISS) and place it back. This will tell the printer to check cartridges again and it will show full and start printing.
With this CISS you will never have to pull a cartridge. If, for some reason you DO need to pull cartridge, make sure the black plastic ink cover key is pulled out FIRST.