I've knitted with beads, and I've found that it's hard to find a needle that is thin enough for the beads but with an eye big enough for the yarn. I read somewhere that you can use nail polish to form the end of the yarn into a point and just thread the beads onto the yarn that way, without a needle. It works like a charm!
If you get to a knot in the yarn, just slide the beads down as far as you can, break the yarn, and re-join past the part of the knot. You won't have to re-string.