Anyone knows if beach worms can be frozen and thawed later when needed? Would it still be usable after being frozen?

Yes.

You can even buy them frozen.

I have never done it. But I f were to I think I would lightly salt them first for an hour or 2. I know the shop bought ones are frozen whole and I am thinking freezing cut might not work to well.

Another pre-freeze trick is alcohol. Again I have not tried it...I have never frozen beach worms...But other similar worms freeze well after soaking in alcohol for about 30 to 60 minutes. A 10 to 15% V/V mix works. Metho is fine. So about 10 to 15 ml ethanol (or methanol) to 100ml water. Soaking in alcohol has a drying affect and also toughens the proteins slightly. I would imagine a higher V/V % would work quicker but would leave an aroma that might put fish off.

You could even try dipping in straight metho (about 95% V/V is normal shop bought) for a minute or so. Then pat dry and salt for 30 minutes and freeze.