If you have access then you can run a new line away from the bathroom, put a new shut off anywhere you want and then return it back to where you started. Think of a big loop with just a shut off on it.

Is there a basement or crawl space underneath?

If you are going to open up everything and shut off the water to replace the valve, the best solution is to put the valve somewhere else. Either up high on the wall so it won’t get wet or turn it to access it from the other side of the wall cavity.