mazal, freezing cooked potato is not recommended (like potato soup) but fried is ok. and since potato kugel has oil, it’s almost like it’s fried (not that mine is so oily, but the theory still works…) what’s really the problem with freezing is that it breaks down the starch in the potato, giving it this weird texture. kugel is already grated, so it can’t really get broken down. besides, there’s no added water, so it’s better… that’s why companies can sell frozen latkes and french fries… if you pay attention to the feel of the potato, you’ll realize that the texture is a bit smoother, more broken down than fresh french fries… but they’re still good!
and you do NOT have to keep the kugel covered in teh oven the whole time when rewarming. if the kugel is defrosted, just rewarm at 350…
if it’s still frozen, cover for 45 min at 400 and then lower the oven temp and uncover… if you keep it covered, it may get soggy.
some people spray the kugel with pam or drizzle with oil before rewarming… you can do what you like.