Welcome, and yea there is no problem with removing a sac. Wakemakers has lots of ballast fittings that could work to just plug the hose so you don't get any water leaking in. Not sure what kind of ballast set up you have, but if you have the older style set up with the sprinkler valves you may want to unscrew the solinoid to that particular sprinkler valve so even if you accidentally hit that button to fill it won't turn on. If you have an updated system with reversible pumps then just take out the fuse. This is the kind of plug that might work, just make sure you get the right size.

https://www.wakemakers.com/flow-rite...-118-plug.html