Hey. I have a gate valve that is damaged and I would like to replace it, or put another one along the pipe line, but the problem is I can't shut off the main water supply. So is there a way to repair this while the water supply is on and the pipe is 2" thick.

the pipe is 2" thick.

If you have a 2" diameter supply line you must be that guy in California with the $500 million complex.

Call the water company, they can turn the water off.

There must be a main valve somewhere that shuts off entire house. Usually, that valve is by the curb, in the ground, right pass the water meter. Since you dealing with 2" pipe, you will need a large tool to turn it off. Unless you turn water off, you will not be able to work on your gate valve.

Advice: Replace gate valve with ball / lever handle / 1/4 turn type valve. Ball type valves are much more reliable.

Milo