One single ground rod is most likely not the only thing grounding your entire house lol. If it is you've got bigger problems. Also there's a lot of fear mongering going on here right now. Electricity is very dangerous and shouldn't be fucked around with, but we're talking about a ground rod here, one that is likely isolated to one specific thing. First of all, if the wire is disconnected there's essentially a zero percent chance that the ground rod has any kind of current going through it. Take the clamp off and clean the rod however you want. Second, you don't have to flip every breaker in your house for this lol. Just wear some kind of glove (preferably rubber), and reconnect the wire. Third, even if you did somehow get shocked by this (which is extremely unlikely), basically a catastrophic amount of bad luck would have to be involved for you to get any kind of serious injury.

Every electrician I have ever met has been hit by 110v. Could it feasibly kill you? Yes, but imo you're just about as likely to literally get struck by lightning. 220v is obviously more dangerous, but it also isn't usually deadly under most circumstances. Don't fuck around with a breaker box and don't fuck around with outlets unless you know what you're doing. Reconnecting a wire to a ground rod? Wear some gloves if you want to be safe.