There is no VBAP-PRICE_FREEZE = 'X' if that's what you are asking for. In the sales order transaction you'll see that the status and consequent documents are checked to determine if certain fields need to be open for input or not.
For price changes there is some SAP note that explains how to implement authorization check for pricing conditions, maybe you could use similar approach to disable the changes? It's FAQ in the SD forum, use Google search.
Also check if something like that is possible using statuses. Similar questions could've been asked in SD forum. Again - Google is your friend.
