Hmm. In principle, you should be able to change your bid each time you post - the ease of change should make things pretty tense. The idea is that by allowing change of bids, we should all converge to numbers that are pretty similar.
Perhaps a good rule would be you can only increase your bid. Game of chicken.
I'm trying to find a way that we can be fair when writing about bid <-> IC actions. For now, the best way is to just ask people to be fair, and use present day purchasing power as a guideline.
What I'll do, for this chapter at least, is have open bids for my company AGS, since the only thing they have is money. If there are some things your company can do to win the bids without openly putting forth money, do that too o_o