Freezing and thawing the prepared custard will likely result in an undesirable texture. However, you can successfully freeze just the egg yolks.
According to the American Egg Board's eggcyclopedia:
The gelation property of egg yolk causes it to thicken or gel when frozen, so you need to give yolks special treatment. If you freeze them as they are, egg yolks will eventually become so gelatinous that they will be almost impossible to use in a recipe.
To help retard this gelation, beat in either 1/8 teaspoon salt or 1
1/2 teaspoons sugar or corn syrup per 1/4 cup of egg yolks (about 4
yolks). Label the container with the number of yolks, the date, and
whether you’ve added salt (for main dishes) or sweetener (for baking
Curiously, in the United States, soft ice cream is sometimes called Frozen Custard. As @Jolenealaska points out, you could make that instead, though it's probably quite different than what you have in mind.