Yes shepherd's pie can be refrozen without any issues.
If you have previously frozen the shepherd's pie and then heated it back up and then only ate some of it and had some leftover shepherd's pie that you want to eat later you can refreeze it as many times as you want too and then reheat it back up.
However the more you reheat the shepherd's pie the more chance you have at overcooking it and it may not be as good.
So it's best to only refreeze the shepherd's pie a few times at most before eating it all.
You can also place the leftover shepherd's pie in the refrigerator if you plan to eat the leftover shepherd's pie within a few days.
Then you can just heat it back up and eat it.