Probably the hardest thing to make when writing a novel is to make or alter a culture. This is even harder if your writing something set far enough in the future for things to be different but not far enough for all the current trends to be washed away.
I tend break down culture to three groups
The first is what I call the transitory level.
This would be things like individual politicians who rise and fall in prominence, or pop stars or anything that last less then a generation then has little effect afterward.
Everything on this level will be completely different in twenty or fifty years. Feel free to change everything here, you hardly even have to justify it.
The second is the core identity level.
This would the things that the culture holds most sacred, truths they hold to be so true they don’t have to prove them. For example “Freedom is important, and is worth dying for.” or “Human life has value and should not be wasted.”
These are often so ingrained they are more emotional then rational. These either shift very slowly, or require a very large impetus to change quickly.
They effect everything about that society, if you change one even a little then you will cause rippling effects that need to be plotted out.
The third is often overlooked, that of biology.
By biology I mean urges and such that we all have, things that push us all whether we want them to or not.
Not to say you can’t fight it, but if you do it pushes back. The best example of this would be the sex drive. One thing that all civilizations have had in common is that they have had whores, often they were not legal, but they were still there.
Even if you go ten thousand years into the future, if humanity is (somehow) unchanged then it will have certain commonalities, certain urges that remain.