Can I play custom positions with my friend?

I think you can only do this if you are a premium member. But there are other websites where you can do this (I will not tell you which one, otherwise we will get blocked).

I think chess.com should change this. I mean, if other websites are allowing people to play a non-rated game from custom position it is obvious that people will go there to do this. There are enough advantages to be a premium member, I think.

I never thought that this feature could "worth" something. Anyway I've found the solution already. I will think about getting premium membership but the only membership that will help me to improve is the diamond membership but the price is quite high. Thank you for the help!

It's possible, but not easy on chess.com. You both agree to make the moves that will take you to the position that you want, and then you play from there.

You can do it in Daily Chess - you just load the desired FEN and off you go.