Can you put egg yolks in the freezer for, let's say, making home made ice cream or custard at a later date?
Yes. No problem.
Certainly. Just be sure to whisk them together first, and when you make the custard at a later date, after cooking it, be sure to strain it. Freezing toughens the membrane around the yolks.
If you whisk in 1 teaspoon of sugar per egg yolk it'll keep the water in the yolks from crystallizing as much, you'll get a better outcome. You just have to remember to exclude the equivalent amount of sugar from the recipe you end up using them in.