In order to affect a change in the cost basis, a sale must occur for proper gain/loss tracking.Sell the S Corp for the cost basis of the new C Corp (the difference in S corp cost basis will be the losses). Buy the C Corp for the same amount the S Corp was sold for. This records the losses from the S Corp and sets up the C Corp with the new proper cost basis and name, and there is no cash balance change in the brokerage journal account where you post the transaction. Make sure you have a detailed memo on each transaction for audit purposes.
This is working on the assumption that the losses incurred from the corp change are to be reflected in the current year taxes.