Can I install an expansion tank on abandoned water softener loop?

After some consideration, I have decided to move my expansion tank from the attic to our insulated garage. There is an old water softener loop in the garage about 12 feet from the hot water heater (water softener was removed years ago by previous owner and loop was left). I have heard that an expansion tank can be added anywhere on the cold side, but I don't know anything about softener loops. There is a cutoff valve on the loop and when shut off it cuts the water throughout the house. Any reason why this wouldn't be a good place to install it? Thanks.

To pass code, the expansion tank should not have any valve between it and the WH. This is to ensure that it always has an open path to the WH to absorb the expansion. From a practical matter, as long as the valve(s) remain open, it will work just fine.

Thanks for the help!