If a candidate is projected to win a state, can that projection change?

Yes. A projection is essentially an educated guess. It’s based on extrapolating current information into the future. That said, most news outlets try not to project a winner until they have pretty strong evidence for their extrapolation. Projections are usually, though not always, correct.

So 218–266 is not necessarily correct???

That’s right. It is not necessarily correct, though it is very likely to be correct. In any case, I wouldn’t expect a concession speech tonight.

Hillary conceded, so probably her people did all the math and didn’t see a way to win.

Yup, she conceded this morning. We’ll probably hear her concession speech sometime later today.

Expert statisticians are very good at crunching the numbers. Their reputations are at stake. It’s unlikely that they could get their prediction wrong when they’ve looked at over 99% of the results.