Sam2: 2 day Yom Tov is not a Minhag. It is a Din D’Rabannan. This is a very important difference. The gimara (beitza 4b and other places) calls it a minhag; top tosafos sukkah 44b proves from here that we can make a b’racha on a minhag.
DY: That’s the Chasam Sofer SDD linked, but it doesn’t answer for modern communication If you mean to say the chasam sofer didn’t realize there would be modern communications when mashiach comes, and had he realized that he wouldn’t have said what he did, then you’re right. I personally wouldn’t want to say that about the chasam sofer.