Things I've learned so far:
* If you back out from the draft after players have been picked, when you resume later the draft will resume at whatever point it was at when you left, so leaving/restarting does no good in terms of erasing mistakes.
* The default setup will replace your starters -- every time you re-select a position on the chart it will start with your starter. This is a bad idea when there's less than 5 seconds on the clock.
* It is possible to change these back via the Depth Chart once the game starts -- drafting a player doesn't replace your existing roster, just changes who initially slots into each position.