I understand that it is not possible to change the postage amount on a multi quantity item after selling one or more pieces with more pieces remaining to be sold.

It is possible to do this on eBay where I used to list prior to coming over to eBid. Perhaps it would be possible to allow postage amount changes in future on eBid?

In this instance I found that the postage amount was less than the actual cost of sending so attempted to amend for further sales.

The only way of changing the postage amount was to stop further sales and relist.